Former governor Tim Kaine’s candidacy in the Virginia open Senate seat has given his party a boost. (Photo by Joe Raedle/Getty Images)

None of that trio is a sure thing but — as we noted a few months back — convincing serious candidates to get into competitive races is a critical piece of Democrats’ strategy to limit their losses (or maybe even make gain) in an election where they have 13 more seats to defend than Republicans.

The candidacies of Kaine, Heinrich and Berkley allow Democratic Senatorial Campaign Committee Chair Patty Murray(Wash.) to go to other spots around the country and cite them as shining examples of how the political environment is turning around for her side.

Democrats clearly hope that renewed optimism will help them grow the playing field into places like Arizona and Texas although the former seems like the far stronger pickup option at the moment. (Click here for our analysis of why Texas is still a very tough state for any Democrat to win in 2012.)

Democrats, of course, need to avoid irrational exuberance given that eight of then ten seats we see as most likely to switch parties in November 2012 are on their side of the aisle.

At the moment, Senate Democrats will take good news where they can get it

As always, the number one ranked race on the Line is considered the most likely to switch party affiliation. Kudos? Critiques? The comments section awaits.

To the Line!

10. New Mexico (Democratic controlled): Rep. Martin Heinrich’s entry into the Democratic primary gives his party a big boost. Heinrich is considered one of the bright young stars in the party, and many see him as the party’s top recruit in the Land of Enchantment. But, state Auditor Hector Balderas is also about to announce a run, which means a competitive Democratic primary. Democratic Senatorial Campaign Committee Chairwoman Patty Murra y (Wash.) notably declined to endorse Heinrich last week. (Previous ranking: 9)

9. Florida (D):State Senate President Mike Haridopolos (R) raised far more money than any other non-incumbent in the first quarter of the year, pulling in $2.6 million from his powerful perch in the state legislature. Unfortunately, Haridopolos has also gotten more bad press than any other candidate, too. That means there’s an opening. Looking to fill it are former state Rep. Adam Hasner, who is garnering some early conservative support, and former Sen. George LeMieux. Democratic Sen. Bill Nelson (D-Fla.), meanwhile, turned in a very strong quarter, raising $2 million and setting himself up for a vigorous defense of his seat. (Previous ranking: 7)

8. Massachusetts (Republican controlled): Democrats made a grand flourish last month when DSCC executive director Guy Cecil made a two-day trip to the Bay State to find a candidate against Sen. Scott Brown (R). But, no candidate has emerged just yet and comments like those made recently by Rep. Barney Frankcautioning Newton Mayor Setti Warren against running — don’t help. Brown’s poll numbers and campaign war chest — $8.3 million as of the end of March — are formidable. But, assuming Democrats can find a credible candidate, the state clearly leans their way particularly in a presidential year. (Previous ranking: 6)

7. Ohio (D): There’s no clear Republican frontrunner here, and Sen. Sherrod Brown is polling well. State Treasurer Josh Mandel, who was elected to his current post in 2010, will almost definitely run, seeing as he’s already hired a fundraiser. He’s also already facing criticism from editorial boards for launching a new campaign only three months into his first statewide job. Former state Sen. Kevin Coughlin is also taking steps towards a bid and former Ohio Secretary of State Ken Blackwell is looking at it. Given recent trends in Ohio, Brown is still beatable. (Previous ranking: 8)

6. Nevada (R): Sen. John Ensign’s resignation has thrown the race into chaos with speculation running rampant that Rep. Dean Heller (R) will be appointed to fill the vacancy by Gov. Brian Sandoval (R). If that happens, it likely strengthens Heller’s hand next fall in the race for a full term (and moves this race further down the Line). On the Democratic side, Berkley finally made it official earlier this month but is likely to face businessman Byron Georgiou, who raised some eyebrows with his impressive first quarter fundraising totals, in a primary. (Previous ranking: 10)

5. Virginia (D): Kaine’s (somewhat) surprising decision to run means that the Commonwealth will play host to the marquee Senate race of the 2012 cycle. While former senator George Allen will have to run a primary campaign, the number of people running against him virtually ensures that the anti-Allen vote will be fractured so as to be ultimately meaningless. Both Kaine and Allen are well known entities in the state and will raise and spend millions. The question is what matters more to voters: Kaine’s support for President Obama as Democratic National Committee Chairman or Allen’s penchant for misstatements. (Previous ranking: 4)

4. Missouri (D): A month after Sen. Claire McCaskill’s (D) tax problems had her looking like a sitting duck, the ostensible GOP frontrunner to face her, state Treasurer Sarah Steelman, announced she had raised just $186,000 in the first quarter.Not good. At all. Reps. Todd Akin and Blaine Luetkemeyer rightly sense opportunity and are weighing the race. Ed Martin, who was the 3rd district nominee in 2010, is also running. (Previous ranking: 3)

3. Montana (D): This race is one of the most settled in the country. Sen. Jon Tester (D) will face off against Rep. Denny Rehberg (R) in a race that all sides consider a pure toss-up. Tester won an early battle when he collected $1.1 million in the first three months of the year to $580,000 for Rehberg. (Rehberg transferred another half million dollars from his House account to a Senate committee to make the differential look smaller.) The fundamental question in this race is whether it is about personalities (in which case Tester will likely win) or about issues (in which Rehberg would be the favorite). (Previous ranking: 4)

2. Nebraska (D): Sen. Ben Nelson raised just over $1 million over the past three months, leaving him with $2.3 million on hand for what’s expected to be a very tough race. State Attorney General Jon Bruning (R) brought in $1.5 million although $600,000 of that was left over from his aborted 2008 Senate campaign. Bruning’s likely primary rivals didn’t fare so well. State Treasurer Don Stenberg took in a paltry $14,000, as did financial adviser Pat Flynn. Stenberg has been attacking Bruning as too liberal and vying for the endorsement of Sen. Jim DeMint (R-S.C.), but for now Bruning looks like the nominee. Nelson’s best hope is that Stenberg keeps the heat on long enough to damage the AG in the primary. (Previous ranking: 1)

1. North Dakota (D): Former Rep. Earl Pomeroy (D) has all but ruled out a bid, saying he’s thinking of running for governor. That’s bad news for Democrats. Republicans don’t have a candidate here yet either, but no matter who they nominate, they have the edge in this open seat. For years, voters have split their tickets in this state, voting Republican at the presidential level but Democratic for Senate. With Sen. K ent Conrad’s retirement, that trend is probably over. (Previous ranking: 2)