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The 10 most competitive Senate races in 2016

Senate Minority Leader Harry Reid (D-Nev.) speaks to reporters on Capitol Hill on March 24. (Pablo Martinez Monsivais/AP)

It's easy to conclude that Democrats are actually in better shape to hold the Nevada seat in 2016 after Sen. Harry Reid's (D) decision not to run for another term.

Reid, after all, had rarely won his races by anything but the skin of his teeth and his role as the leading national Democratic in the Senate had badly tainted his image back in the state. He won in 2010 in no small part because Republicans nominated the single worst candidate to run in that election — or maybe any recent election.

All true. And yet, the most fundamental truth of politics is that it's damn hard to beat an incumbent.

Reid's presence in the race was already making it difficult for Republicans to recruit a top tier challenger against him. While Gov. Brian Sandoval (R) was never going to run — and I would be stunned if he reconsiders that decision in the wake of Reid's announcement — the prospect of facing Reid and his political machine was decidedly daunting for any up-and-coming Republican.

That major impediment has now been removed. Sure, Reid is making moves — endorsing former state Attorney General Catherine Cortez Masto, for one — that suggest that he will be engaged in the race to succeed him. But there is a big difference between running against Harry Reid and running against a candidate Harry Reid supports.  One is scary; the other is less so. (Sandoval proved that point when he drubbed Rory Reid, the senator's son, to win the governor's race in 2010.)

The field — for both parties — is still very much taking shape. GOP Rep. Joe Heck, a well-regarded pol, has to be seen as more likely to run in an open seat than against Reid.  Adam Laxalt, the newly elected state attorney general, grandson of longtime Nevada Sen. Paul Laxalt and the illegitimate son of former New Mexico Sen. Pete Domenici, also would have to be more interested in a Reid-less race.

Point is: Reid was a known (and feared) commodity among Nevada Republicans. Cortez Masto, assuming she runs, doesn't inspire those same feelings of trepidation. And that's a good thing for Republicans eyeing the state as a pickup.

Below are the 10 races considered the most likely to switch parties in 2016. The number one race is — you guessed it! — the most likely to switch.

10. Indiana (R)Sen. Dan Coats’s (R) unsurprising retirement this week puts this seat on the Line for now, in large part because it’s an open seat. But just because Democrats pulled the upset here in 2012 doesn’t mean they’ll be favored to again. They got a lot of help from Richard Mourdock and his comments about rape. Barring a run from former senator Evan Bayh (D) and his $9.9 million campaign account, Republicans should be favored in this red state. (Previous ranking: N/A)

9. North Carolina (R): Sen. Richard Burr (R) voted this week like a senator who was very conscious of his reelection campaign in 2016, but this isn’t really considered a top Democratic target just yet. The big question here is whether Democrats can secure a big-name nominee to run alongside Attorney General Roy Cooper (D) in the governor’s race. (Previous ranking: 9)

8. Ohio (R): Democrats got their man when former governor Ted Strickland decided to run. But Cincinnati City Councilman P.G. Sittenfeld shows no signs of getting out of the primary and could hurt Strickland some by making it a new-vs.-old dynamic. (Strickland is 73; Sittenfeld is 30.) Strickland remains a strong favorite given his fundraising capacity and the depth of endorsements he has won from Democrats. But it's not entirely clear how vulnerable Sen. Rob Portman (R) actually is. Yes, Ohio is and will be a swing state. But Portman has positioned himself in the ideological middle and is one of the most capable campaigners in Washington. (Previous ranking: 7)

7. New Hampshire (R): Nothing will happen in this race until Gov. Maggie Hassan (D) makes up her mind on challenging Sen. Kelly Ayotte (R). That decision isn't likely to come until mid-summer when the state budget fight wraps. If Democrats don't get Hassan, this race will drop down the Line.  Another interesting twist to keep an eye on: Ayotte will almost certainly be in the mix to be the vice presidential pick for Republicans. (Previous ranking: 6)

6. Florida (R)This seat is as high on the Line as it is because (1) Sen. Marco Rubio (R) probably needs to vacate it in order to run for president – which seems likely – and (2) Democratic Rep. Patrick Murphy just got in the race. The young congressman, though, might face a contested primary with controversial Rep. Alan Grayson, who could pull him to the left (and would be a disastrous nominee if he somehow won the primary.) (Previous ranking: 8)

5. Colorado (Democratic controlled): With Reid's retirement, the only Democratic incumbent running in 2016 in any danger of losing is Michael Bennet. Bennet, like Reid, won an unlikely victory in 2010 — a year that was disastrous for Democrats nationally. Bennet will, once again, be a major target but it's not at all clear yet who Republicans will field as their candidate. The most talked-about option is Rep. Mike Coffman, but who knows whether he will run. Republicans will find someone but, as 2010 proved, they will need someone better than Ken Buck to beat Bennet. (Previous ranking: 5)

4. Pennsylvania (R): Democrats have made no secret of their discontent with the idea of former Rep. Joe Sestak, who lost to Sen. Pat Toomey (R) in 2010, as their nominee again next year.  But, they don't appear to have any alternatives worth mentioning — even as Sestak has launched his campaign by walking across the state.  We've long held that Toomey's political skills are underrated but this will be a very tough race given presidential year turnout in the clearly Democratic-leaning Keystone State. (Previous ranking: 4)

3. Wisconsin (R): A recent poll from Democratic-leaning automated pollster Public Policy Polling showed former senator Russ Feingold (D) leading Sen. Ron Johnson (R) 50 percent to 41 percent. Three Democratic members of Congress, though, all trailed Johnson by between six and eight points. Feingold seems increasingly likely to run. (Previous ranking: 2)

2. Nevada (D): See above. (Previous ranking: 3)

1. Illinois (R): Sen. Mark Kirk (R) is endangered in a blue state, and it doesn’t help that tea party former congressman Joe Walsh is considering a primary challenge. On the Democratic side, keep an eye on Rep. Tammy Duckworth in the weeks ahead. (Previous ranking: 1)