The U.S. Senate is very much in play in the 2012 election.

In fact, it’s so much in play that Guy Cecil, the executive director of the Democratic Senatorial Campaign Committee, recently remarked that there was a 50 percent chance Republicans will reclaim the chamber.

Sen. Claire McCaskill (D-Mo.) speaks during a roundtable discussion on the campus of the University of Central Missouri, in Warrensburg, Mo. (Julie Denesha/FOR THE WASHINGTON POST)

But with upwards of a dozen or more races looking potentially competitive right now, paying attention to every race is nearly impossible.

So The Fix, in true Fix fashion, has distilled the battle for the Senate down to three key questions, after the jump.

* What’s the down-ballot effect?

One interesting thing about the 2012 Senate campaign — as we’ve noted before — is that most of the top races are outside of the swing states. That means the presidential race matters.

But just how much does it matter?

Likewise, Democrats including former senator Bob Kerrey of Nebraska, former North Dakota attorney general Heidi Heitkamp (N.D.) and Sens, Claire McCaskill (Mo.) and Jon Tester (Mont.) will all have to significantly over-perform the top of the ticket in states where Obama could lose by wide margins — perhaps double digits. Ditto former Hawaii governor Linda Lingle (R), who may be the best example of all in President Obama’s birth state, where the president took 72 percent of the vote last time.

In 2008, Obama’s success at the top of the ticket certainly helped now-Sens. Kay Hagan (D-N.C.) and Jeff Merkley (D-Ore.), who, despite being little-known state legislators, knocked off incumbents.

* How do GOP candidates pan out?

Republicans have a lot of opportunity but also a lot of candidates who have something to prove. This group includes insurgent primary candidates such as Indiana state treasurer Richard Mourdock and Nebraska State Sen. Deb Fischer, who are still expected to win after knocking off establishment-favored candidates. The same goes for Rep. Rick Berg (R-N.D.), whose personal approval ratings aren’t great.

But if the GOP loses races like these, it’s already lost the majority.

The bigger questions when it comes to control of the chamber are Florida Rep. Connie Mack, Ohio state treasurer Josh Mandel and the crowded fields of candidates in Missouri and Wisconsin. The uncertainty in the latter two states in particular — the Missouri GOP primary is a jumbled mess, while former Wisconsin governor Tommy Thompson faces several opponents and has problems on his right flank — will go a long way toward determining whether Republicans have the number of pickup opportunities they need to take the Senate.

* How big (and expensive) is the map?

If Arizona and Indiana come into play, the GOP’s task of gaining a majority becomes much tougher. And if Hawaii, Florida and Ohio come into play, Democrats will have a really hard time holding the majority.

If all of them come into play, we are in for a Senate election the likes of which we have rarely seen, with nearly half of the 33 seats being genuinely competitive.

The more seats that come into play, the more money and strategy matter at the national level, and the more those parties will be begging donors to send money to Senate races instead of the presidential contest.

Republicans have a big edge in super PAC spending, and if the map gets really big, Democrats will likely need to pick up the slack. On the other hand, Democrats have more incumbents and experienced candidates to rely on.

Keep an eye on these three things, and you should have a pretty good idea in which direction things are headed.

To the line!

10. New Mexico (Democratic-controlled): Rep. Martin Heinrich (D) faces a primary fight on Tuesday but is expected to win easily. Former congresswoman Heather Wilson will be the Republican nominee and is, without question, the GOP’s strongest candidate and best chance to win statewide in the Land of Enchantment. But this is New Mexico in a presidential year, and it remains to be seen whether Wilson can overcome what is expected to be a victory for Obama. Still, she has done everything right to this point and has a history of running very credible campaigns in a tough House district. (Previous ranking: 8)

9. Virginia (D): The good news for former senator George Allen is that he didn’t run into a serious tea party primary challenger, and he’s virtually assured of winning the GOP nomination 11 days from now. The bad news is that the last few polls here have shown Obama holding on to a lead in the Commonwealth. We’ve said it before and we’ll say it again: It’s hard to believe that Obama voters would cross over to vote for Allen. We expect this Senate race to closely mirror the presidential. (Previous ranking: 9)

8. Wisconsin (D): We’ve been a little slow to the party in moving this up the GOP’s list of top-tier targets, but we’re starting to believe a little bit. That’s in no small part thanks to Gov. Scott Walker’s (R) strength in next week’s recall and Mitt Romney polling neck-and-neck with Obama. Early Senate polls also show the GOP with a lead; the problem is that the party is headed for a rough-and-tumble primary, while Democratic Rep. Tammy Baldwin is amassing lots of money. Still, we should consider this one a toss-up. (Previous ranking: 10)

7. Nevada (Republican-controlled): The latest NBC/Marist poll shows Sen. Dean Heller (R) and Rep. Shelley Berkley (D) tied. No surprise here. Worth noting, though: Berkley is only winning Hispanic voters 57 percent to 39 percent. In 2010, Senate Majority Leader Harry Reid took 69 percent of Hispanic voters. Berkley will have to do better with Latinos to beat Heller. (Previous ranking: 7)

6. Massachusetts (R): It’s been a rough month for Elizabeth Warren, who continues to struggle to get out from under questions about when she told her employers that she had Native American heritage. Warren won’t lose the election to Brown because of her ham-handed handling of this issue, but it suggests that she remains an inexperienced candidate embroiled in the highest-profile Senate race in the country. Brown is running as a nonpartisan, airing ads touting Fenway Park and retiring Red Sox players (not kidding) that make zero mention of his party. It’s a smart strategy but one Warren won’t let him get away with for long. (previous ranking: 6)

5. Montana (D): New month, same race. Tester has a cash-on-hand edge of roughly $1.5 million over Rep. Denny Rehberg (R). But aside from that, the race is about as close as close can be in every measurable category. Tester launched an ad playing up how he brings Montana beef with him to Washington; Rehberg responded with an ad saying Tester brings Washington “baloney” back to Montana. Montana could well be the contest that decides which party controls the Senate, but it is decidedly low on the national radar at the moment. (Previous ranking: 5)

4. Missouri (D): Sen. Claire McCaskill (D) continues to get pummeled by the outside GOP group American Crossroads, which just went up with another new ad coining the term “ObamaClaire.” (Get it? Obamacare?) She’s hoping to use general dislike of super PACs to her own advantage, but it’s a tough strategy, since voters rarely decide based on campaign finance arguments. A Democratic poll released early last month showed her leading all comers, but all other polling has shown she has a tougher race in front of her. (Previous ranking: 4)

3. North Dakota (D): Democrats have released two polls – one from the Democratic Senatorial Campaign Committee and one from the state party – showing Heidi Heitkamp leading Rep. Rick Berg by five points. And the only independent poll – which had Berg up seven points – appeared to have some methodological problems. What’s clear: Berg will not sail into the Senate. While it might be tough to call this is a toss-up, it’s certainly not a done deal for the GOP in a conservative state. (Previous ranking: 3)

2. Nebraska (D): Democrats are trying to spin Deb Fischer’s GOP primary win as a boon to Bob Kerrey. After all, state Attorney General Jon Bruning was the better-known, better-funded GOP candidate in the race. But Fischer does not have any of Bruning’s negatives, which are a big reason he lost the primary. As long as Fischer doesn’t have any skeletons of her own, Kerrey's slim chance at victory may have gotten even slimmer. (Previous ranking: 1)

1. Maine (R): We know two things here. First is that former governor Angus King (I) is a heavy, heavy favorite, leading in the only public poll of this race by more than 30 points. And second, we are pretty darn sure that he won’t caucus with Republicans. If both hold true, this will grace the top of our list for the remainder of the election cycle. (Previous ranking: 2)

Chris Cillizza and Rachel Weiner contributed to this report.