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A1: The stories you need to read before your first conference call.

-- The U.N. says hundreds of civilians were killed in a massacre in Bentiu, the capital of South Sudan's oil-producing north, by soldiers loyal to rebel leader Riek Machar. A statement issued late Tuesday by White House spokesman Jay Carney condemned the violence; bulldozers had to be used to clear away the dead. A U.N. refuge camp in Bentiu is now home to 22,000 people, a five-fold increase since the beginning of April. (Associated Press, Washington Post)

-- Sen. John Boozman (R-Ark.) is recovering in intensive care after undergoing unscheduled heart surgery Tuesday morning after an aortic aneurysm. Boozman was taken to the hospital early yesterday after experiencing pains in his chest and arms; the procedure lasted several hours, a spokesman said. (Northwest Arkansas Business Journal)

-- Democrats and Republicans are largely bypassing records of the candidates they're running, and running against, and focusing instead on their allies -- the "boogeyman billionaires against the shifty septuagenarian." Democrats will attack the Koch brothers, while Republicans will elevate Senate Majority Leader Harry Reid. Few voters know Reid, but the GOP wants to make him the next Nancy Pelosi. (Associated Press)

-- A first round of Upshot/Kaiser Family Foundation Senate race polls shows Sen. Mark Pryor (D-Ark.) leading Rep. Tom Cotton (R) 46 percent to 36 percent; Sen. Kay Hagan (D-N.C.) leading state House Speaker Thom Tillis (R) 42 percent to 40 percent; Sen. Mitch McConnell (R-Ky.) leading Secretary of State Alison Lundergan Grimes (D) 44 percent to 43 percent; and Sen. Mary Landrieu (D-La.) leading Rep. Bill Cassidy (R) 42 percent to 18 percent -- still well short of the 50 percent she needs to hit to avoid a runoff.

-- Scary moments for Democrats in Arkansas, Louisiana and North Carolina: A majority in each state say they wouldn't vote for a candidate who doesn't share their views on the Affordable Care Act. And those who say they're voting Republican also say they're more likely to vote. (New York Times)

-- The DNC has asked Atlanta, Chicago, Cleveland, Columbus, Detroit, Indianapolis, Las Vegas, Miami, Nashville, New York, Orlando, Philadelphia, Phoenix, Pittsburgh and Salt Lake City to submit proposals to host the party's 2016 nominating convention. (CNN, Washington Post) Cleveland and Las Vegas are the only two cities in the running for both the Dem and GOP conventions.

-- Supreme Court justices on Tuesday expressed skepticism over an Ohio law that attempts to regulate false statements made during political campaigns. The Court doesn't have to rule on the constitutionality of the law, because the case revolves around whether a conservative group has standing to challenge it. (Associated Press) The Court on Tuesday also said states are free to prohibit the use of racial considerations in university admissions, upholding a 2006 Michigan constitutional amendment. (Washington Post)

-- Front Pages: WaPo, NYT and WSJ all lead with SCOTUS's Michigan decision. Check out the Detroit News and the Lansing State Journal ("UPHELD"). USA Today looks at background check shortfalls in gun sales.

National Roundup: What's happening outside the Beltway.

-- Florida: Businessman Curt Clawson (R) took 38.2 percent of the vote to win a special Republican primary to replace former Rep. Trey Radel (R) in a southwest district stretching from Fort Myers south to Naples. Clawson spent $1.5 million on ads, far more than two state legislators he beat. Outside groups weighed in with more than $2.6 million in spending. Clawson is expected to easily beat Democratic nominee April Freeman in the June 24 special election. (Ft. Myers News-Press)

-- North Carolina: Republicans running for the right to face Sen. Kay Hagan (D) in November met for their first televised debate Tuesday, where state House Speaker Thom Tillis (R) weathered a few slings and arrows as his rivals mostly focused on their own messages. The Republicans will meet again Wednesday and next Monday. (Raleigh News & Observer) Reid's Take: The Chamber of Commerce has delayed its endorsement of Tillis, ostensibly over scheduling conflicts. We can't help wonder if the prospects for a runoff are rising.

-- South Carolina: Sen. Lindsey Graham (R) urged House Speaker John Boehner to give Rep. Mick Mulvaney (R) a seat on the House Financial Services Committee, a move that helped ensure the rising star in Palmetto conservative circles wouldn't run for Graham's Senate seat. Graham has spent $1 million on TV ads and recruited 2,500 precinct captains, even though he doesn't face an A-list challenger; he's trying to get 50 percent in the June 10 primary to avoid a runoff. (Politico)

-- Nebraska: Sen. Ted Cruz (R-Texas) really, really doesn't get involved in contested primaries, he swears. Except maybe in Nebraska, where Cruz endorsed wealthy businessman Pete Ricketts (R) in the governor's race and former Bush administration official Ben Sasse (R) in the Senate primary. (Lincoln Journal Star, Sasse campaign release) No one tell John Cornyn.

-- Colorado: Yesterday, we told you Sen. Mark Udall was going on air with $400,000 in broadcast and cable ad time. Here's the ad, a negative spot hitting Rep. Cory Gardner (R) on birth control and abortion. (Denver Post)

-- Wisconsin: A wealthy Milwaukee-area couple with a history of backing Gov. Scott Walker (R) gave $1 million to the Republican Governors Association eleven days before the RGA transferred the same amount to a PAC running ads on Walker's behalf. The RGA doesn't earmark contributions, a spokesman said, but expect the ads against former state Commerce Secretary Mary Burke (D) to continue. (Milwaukee Journal Sentinel)

-- Virginia: State legislators return to Richmond today for a veto session, but there's no bipartisan agreement in sight on a two-year, $96 billion budget or an expansion of Medicaid, a top priority of Gov. Terry McAuliffe (D). That means the commonwealth is likely headed for a government shutdown. The Republican-led House and Democratic-led Senate haven't even taken up each other's budget, which means they can't hold a conference committee to hash out differences. (Washington Post)

DC Digest: What's on tap today in DC.

-- President Obama landed in Tokyo around 6 a.m. EST, 7 p.m. local time, for the first stop on his Asia tour. Obama will have dinner with Prime Minister Shinzo Abe before calling it a night just as Washington's day gets started. Vice President Biden, back from meetings in Ukraine, has a full day at the White House with no public events.

-- A House oversight subcommittee run by Rep. John Mica (R-Fla.) in May will hold hearings over D.C.'s move to decriminalize marijuana, a possible first step toward overturning the city council-passed measure. Congress has 60 days to veto any measures passed by the D.C. council, a period that expires in mid-July. (Washington Post)

TV Time Out: Our exclusive look at who's advertising, and where

-- Louisiana: Democratic super PAC Patriot Majority has purchased $168,000 for ads defending Sen. Mary Landrieu (D), to run statewide between April 24 and April 30. It's the latest group to parachute onto Louisiana TV: Senate Majority PAC has already run $1 million in ads for Landrieu, while two groups linked to the Koch brothers has spent $1.7 million against her.

-- Nebraska: The Club for Growth began running $50,000 in ads for former Bush administration official Ben Sasse (R) yesterday. Sasse is spending almost as much on his own ads for the week of April 22-28, while state Treasurer Shane Osborn is up with $70,000 in ads. A third candidate, bank president Sid Dinsdale, is spending just under $5,000 this week on cable. Osborn has spent the most on TV, almost $200,000 more than Sasse, but Sasse leads in most polling.

-- New Hampshire: Here comes Americans for Prosperity. The conservative group on Tuesday purchased almost $450,000 in ads hitting Sen. Jeanne Shaheen. The new round of ads will run from April 24 to May 12, at a rate of about $150,000 a week, on Manchester broadcast and Boston cable channels. Shaheen's allies have been off the air since the middle of February.

-- North Carolina: Clay Aiken is back on TV, and this time he's not on American Idol. Aiken's long-shot campaign against Rep. Renee Ellmers (R) is spending $40,000 on a 30-second bio spot set to run in advance of next month's primary. (Roll Call)

The Buried Lede: The nuggets that deserve the spotlight.

-- The GOP's demographics problem "is … almost certain to get worse unless something big changes. As in, the 2016 presidential election will be a tough one for Republicans to win given the demographic changes in the country but it won't be nearly as difficult for them as the 2024 or 2028 elections could be." (Washington Post)

-- Reid's Take: The speed of demographic change means Republicans just can't win national elections if they can only manage 27 percent of the Hispanic vote and 6 percent of the African American vote. The white share of the electorate is declining rapidly enough that the GOP has to make new inroads if it ever wants to elect another president.

B1: Business, politics and the business of politics

-- Lobbying revenue continued to recover in the first quarter of the year, but at a slow pace amid languid legislative sessions on Capitol Hill. Patton Boggs, the biggest earner on K Street, saw its revenue decline slightly while laying off 19 lobbyists. K&L Gates, Akin Gump, Covington & Burling, Brownstein Hyatt Farber Schreck, and Van Scoyoc all posted year-over-year gains, raking in more than seven figures on first-quarter lobbying receipts. (Politico)

-- The Navy is once again on the verge of awarding a multi-billion dollar contract to build a new fleet of Marine One helicopters to ferry the president around. The Pentagon killed the last program, which hit massive delays and cost overruns, in 2009; this time, the Navy promises to get the job done for "significantly less" than the $13 billion it cost last time. (Washington Post)

-- Markets are mixed in early morning trading after making gains on Tuesday. The Nikkei is up a point while European markets are trading slightly lower. (CNN)

C1: The long reads you'll need to check out before tonight's cocktail party.

-- A simple explanation for all those negative ads: In an era of hyper-partisanship, persuasion campaigns are less effective than mobilization campaigns. Negative ads depress turnout, and controlling the makeup of the electorate is a more effective strategy than winning over the relatively small number of undecided voters. Smart post from UCLA Professor Lynn Vavreck at the New York Times.

-- More evidence of the polarized electorate: Just 26 House districts split their vote between the parties on presidential and House races in 2012 (as in, voting Republican for President and Democratic for Congress, or vice versa). That's lower than any election since 1920, when just 11 districts split their vote, according to the latest edition of Vital Statistics on Congress. (Washington Post)

C4: The comics page, fun things to read when you're bored at work

-- "When you're 90, you don't order room service," former Senate Majority Leader Bob Dole quips. More Dole, on emulating Sen. Strom Thurmond's eating habits: "When he ate a banana, I ate a banana. And he made it to 100."

-- Dole is on a state-wide thank-you tour in Kansas, with nine stops planned this week and 16 planned next month. Dole, asked about the GOP's 2016 field: "I think they lack experience. … So I'm hoping someone will come along who has a lot of good common sense and good values and listens to people." (Washington Post)

-- Holy guacamole! A truck carrying 33,000 pounds of avocados flipped over on Interstate 65 near Cross Plains, Tenn., on Tuesday. The driver wasn't injured, and crews hoped many of the avocados would still be salvageable. (The Tennessean)

Attn Matt Drudge: Things conservatives will get outraged by today.

-- Four counties in central Alabama -- Macon, Lowndes, Wilcox and Greene -- have more registered voters than actual adults, which Secretary of State Jim Bennett says is a recipe for voter fraud. Another eight counties have a disproportionately high percentage of registered voters. The discrepancy could simply be a case of Census undercounting. But never fear, fraud-watchers: Alabama's new voter ID legislation goes into effect for the first time when voters head to the polls for the June 3 primary. (Birmingham News)

-- The next big government boogeyman: The Bureau of Land Management. In the wake of the Cliven Bundy standoff in Nevada, the Republican nominee for Texas Agriculture Commissioner is warning that BLM is eyeing a takeover of 90,000 acres of land along the Texas-Oklahoma border, which BLM says may not have been Texas's to give away in the first place. (Breitbart) Next step in the conspiracy theory progression chart: Complaints that BLM is buying millions of rounds of ammunition.

Attn HuffPo: What outrages liberals today

-- Was Media Matters paid to target former CBS News reporter Sharyl Attkisson? That's the claim she made this weekend on CNN. But Media Matters chairman David Brock categorically denied the charge in an email to Attkisson on Monday and demanded that Attkisson either show evidence or publicly apologize. (TPM)

-- Oxford, Miss., Mayor Pat Patterson says his city can attract a more diverse crowd of shoppers if more dollar stores opened up downtown. "If there were Dollar Generals and Family Dollars out there, you'd have different demographics," Patterson told a student news channel at the University of Mississippi. Apology coming in 3, 2, 1… (Jackson Clarion-Ledger)