Montana Gov. Steve Bullock (D) just gave his party a boost in the battle for the Senate.

Sen. Max Baucus (D-Mont.), above, is leaving the Senate for China. (Michael Reynolds/EPA) Sen. Max Baucus (D-Mont.), above, is leaving the Senate for China. (Michael Reynolds/EPA)

By appointing Lt. Gov. John Walsh (D) to the upper chamber Friday, Bullock elevated an underdog Senate contender to a sitting senator. Now, Walsh will have the advantage of incumbency in one of the highest-stakes races in the battle for the majority.

Walsh will replace Sen. Max Baucus (D-Mont.), who was confirmed Thursday as the next U.S. ambassador to China. Walsh is also a candidate for the Senate in the November midterm election. A strong Republican recruit and the natural conservative tilt of the state have turned the race into a golden pickup opportunity for the GOP. Republicans still have the advantage there, but Bullock's move has whittled it.

It's a significant development in the battle for the Senate. Republicans need to pick up six seats to win the majority in November. Montana is one of three open seats, along with West Virginia and South Dakota, that are viewed as must-wins for the GOP.

When he heads to Washington, Walsh will have greater visibility and name recognition back home. He'll also have better access to donors by virtue of his new power, as well as a chance to establish a voting record.

For someone like Walsh who isn't a household name in Montana politics, these would all be assets. But he will also have to fend off inevitable claims about power grabbing and backroom deals that will come from the opposition. Walsh is facing former lieutenant governor John Bohlinger in the primary. In the general election, the likely GOP nominee will be Rep. Steve Daines.

Just look at what Democrats tried to do to Sen. Dean Heller (R-Nev.). After Heller was appointed in 2011, Democrats swiftly cast him as "unelected" Sen. Heller. But Heller was able to survive such attacks. The question is whether Walsh can survive them, too.

Another factor to keep in mind: Appointed senators who run for their seats have only been elected about half the time, a University of Minnesota Smart Politics analysis shows. Being appointed and having a full term under your belt are very different things in the eyes of voters.

But on the whole, it's a good day for Democrats in Montana and Washington, D.C.. Montana remains a tall climb for the party, but it's not as steep as it once looked.

Below is our latest rundown of the top 10 races most likely to change party control. As always, No. 1 is the seat most likely to flip.

To the Line!

10. Georgia (Republican-controlled) and Michigan (Democratic-controlled): Georgia Democrat Michelle Nunn and Michigan Republican Terri Lynn Land each had very productive fourth-quarter fundraising periods. Both hit the seven-figure mark, putting pressure on the opposing parties, which remain favored to win these seats. Polling out of Georgia this week showed a wide open race for the GOP nomination -- which is good news for Nunn. The more competitive/expensive that race becomes, the better for her. Meanwhile, in Michigan, likely Democratic nominee Rep. Gary Peters (D) is appearing with President Obama Friday -- a reminder that not every candidate is running far, far away from him. (Previous rankings: 10)

9. Iowa (D): There was a time when it looked like state Sen. Joni Ernst had the inside track for the Republican nomination. She is, after all, the unofficial favorite of Gov. Terry Branstad (R). But the field looks more fluid now, as Ernst has put up somewhat lackluster fundraising numbers. That said, the GOP field as a whole has also been underwhelming, and Ernst has outraised everyone and has more cash on hand than Mark Jacobs (R), who put up an impressive fourth quarter showing but also has a high burn rate. Likely Democratic nominee Rep. Bruce Braley, meanwhile, had another good fundraising quarter. Sen. Tom Harkin (D) is retiring in Iowa. (Previous ranking: 9)


8. North Carolina (D): Amid the troubled rollout of Obamacare, Democratic Sen. Kay Hagan's image took a hit. It doesn't help her that Republican groups have been slamming her over the airwaves. But Republican front-runner Thom Tillis had a disappointing fundraising period, even as he got a hand from some top figures in the party. Hagan, for her part, put up a big $2 million quarter. (Previous ranking: 7)

7. Kentucky (R): Secretary of State Alison Lundergan Grimes (D) kept up a strong fundraising pace in her second quarter as a candidate, pulling in $2.1 million – slightly less than Senate Minority Leader Mitch McConnell's (R) $2.2 million. She’s also banking a good portion of what she’s raised – about 75 percent. We’re still really waiting to see how good she is on the stump, but she could have suffered a fundraising letdown, and she didn’t. An autodial poll released Thursday showed Grimes with a slight lead over McConnell. (Previous ranking: 8)

6. Louisiana (D): The tea party candidate seeking to upend Rep. Bill Cassidy (R) and make the runoff with Sen. Mary Landrieu (D) – Rob Maness – raised just $240,000 in the fourth quarter. That’s real money, but it’s not great. At this point, Maness appears to be more of a nuisance than a real competitor, but given the runoff is a one-month sprint, his presence still probably hurts Cassidy by diverting attention from Landrieu – at least to some degree. (Previous ranking: 6)

5. Alaska (D): Some good news for the GOP: A clear fundraising front-runner appears to have emerged in former attorney general Dan Sullivan. Sullivan outraised Lt. Gov. Mead Treadwell (R) $1.2 million to $228,000, with 2010 nominee Joe Miller raising a measly $30,000. If Sullivan can leave the field in his wake, that will leave him more time to focus on Sen. Mark Begich (D) in this red state. (For what it’s worth, Sullivan also outraised Begich, who pulled in $850,000.) (Previous ranking: 5)

4. Arkansas (D): Sen. Mark Pryor (D) has no longer been spared attacks from Americans for Prosperity. The well-funded GOP group targeted him over the airwaves this week, adding to his worries. His opponent, Rep. Tom Cotton (R), meanwhile, turned heads by being the only member of the state's all-GOP House delegation to vote against the farm bill. (Previous ranking: 4)

3. Montana (D): Things are looking up for Democrats here with Walsh headed to the Senate. But it's still a slightly better pickup opportunity for Republicans than Arkansas. It will be interesting to watch how Walsh navigates big votes in Washington. Coming from a conservative state, it would be reasonable to expect to see him try to put distance between himself and the Obama administration in a tangible way. (Previous ranking: 3)

2. West Virginia (D): Thanks to a sizeable head start, Rep. Shelley Moore Capito (R) has outraised Secretary of State Natalie Tennant (D) $4.9 million to $800,000 so far. Tennant, as a statewide official, certainly gives Democrats some hope here, but Capito seems solid so far, and this is a heavily conservative state. Unless your name is Joe Manchin or Nick Joe Rahall, that means it’s very tough to win a federal race as a Democrat. (Previous ranking: 2)

1. South Dakota (D): The likely Democratic nominee, Rick Weiland, raised just $161,000 in the fourth quarter despite some high-profile support from former Dakota senators including his former boss, Tom Daschle. If Weiland’s quarter wasn’t so underwhelming, we might be talking about how former governor Mike Rounds (R) had another not-so-great quarter at $516,000 raised. About the best Democrats can hope for right now is for former Sen. Larry Pressler (R) to run a legitimate independent campaign and steal lots of votes from Rounds. Pressler got in late in December and seeded his campaign with less than $30,000. (Previous ranking: 1)

Updated at 4:10 p.m. with more detail about fundraising in the Iowa Senate race