New Hampshire Gov. Maggie Hassan, second from left, who won reelection in 2014, is now running for Senate, leaving an open seat Republicans are keen to win this year. (Jim Cole/AP)

Last Friday, we wrote that the Senate map for Democrats provides them several plausible paths to take back control of the chamber in November.

But when it comes to governors' races, Democrats are playing all kinds of defense. They hold eight of the 12 contested seats this year, and five of their governors are retiring or stepping down, putting at least three Democratic-controlled seats in play for Republicans.

Democrats' best chances to flip seats from red to blue go through two Republican governors weakened by legislative drama back home. And as Politico's Kevin Robillard has pointed out, defeating a sitting governor is one of the hardest things to do in politics. Sitting governors have won reelection in 50 of the past 53 attempts.

The state of play for governors' races looks even rosier for Republicans when zooming out even further. They currently dominate the governors' mansions, controlling 31 of the 50. A few vulnerable GOP incumbents aside, if Republicans can win just one of the contested open seats, they will match their post-World War II record of controlling 32 governors' mansions.

Enough chatter; here are the top five governors' races. They're listed in order of least likely to most likely to flip parties in November, with No. 1 being tops.

To the line!

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5. Indiana (Republican held): Indiana wouldn't have made our list had everything gone according to plan for Republican Gov. Mike Pence, who is running for a second term in a red-leaning state. But Pence saw himself at the center of a national controversy last year when he signed a religious freedom bill. He said it would protect religious business owners in the wake of the Supreme Court legalizing same-sex marriage; opponents claimed it would codify discrimination. Pence eventually signed a revised version banning discrimination based on sexual orientation. But not before his approval ratings plummeted and the state's largest city, Indianapolis, was estimated to have lost $60 million in economic investment in the aftermath.

A weakened Pence will face a rematch with Democrat and businessman John Gregg, who has described himself as a "gun-totin,’ Bible-quotin,’ Southern Indiana Democrat." Gregg lost to Pence in 2012 by 3.2 percentage points, in an election in which Pence failed to get 50 percent of the vote.

4. North Carolina (R): Republican Pat McCrory is running for a second term in a race that is shaping up to be less a referendum on McCrory and more a referendum on the Republicans' super majority in the state legislature and their hold on most of the state government. Since sweeping state government in 2012, North Carolina Republican lawmakers have expanded where you can openly carry a gun, slashed unemployment benefits, put more restrictions on abortion providers and implemented Voter ID laws (which are now being litigated in court).

Presidential politics will also play a role here. If Hillary Clinton's nomination can rally black voters in the state, McCrory might have to play defense to keep his seat, a feat made more difficult if Donald Trump is the nominee. McCrory also faces questions about his conduct when it comes to whether he intervened in a prison contract to help a friend and donors. Once he gets through his primary, his biggest challenger will be Attorney General Roy Cooper, a long-sought-after candidate for North Carolina Democrats who is keeping pace in the money race. (As an update, Cooper's campaign points out they've out raised McCrory 14 months in a row, most recently with $1.4 million in the bank than the governor.)

3. New Hampshire (D): This is another race that wouldn't have made our list but for the actions of the current governor. Popular Democratic Gov. Maggie Hassan has decided to leave her seat to challenge Sen. Kelly Ayotte (R) in what will be one of the Senate's marquee 2016 races. The race to replace Hassan is a toss-up. Republicans are hopeful to take back the seat for the first time in a decade with none other than the son of a former governor, Executive Councilor Chris Sununu. He's first got to win a primary against state Rep. Frank Edelblut. Democrats have their own primary with another executive councilor, Colin Van Ostern of Concord, who is popular with progressive groups in the state. He'll be facing Mark Connolly, the former New Hampshire deputy secretary of state, in the primary.

Even though the best-known name in this race is on the Republican side, New Hampshire Republicans have won just one governor's race in the past two decades (and that's in a state that has them every two years). Like the Senate race, what happens will likely be shaped by the winds of the unpredictable presidential race. It's a pure toss-up.

2. West Virginia (D): Democratic Gov. Earl Ray Tomblin is term-limited, giving Republicans a chance to continue their steady march to paint the state red, much like Republicans have in neighboring Kentucky. Obama lost the state by double digits twice, and all but one of West Virginia's five-person congressional delegation are Republicans. The state legislature is now controlled by Republicans as well. The politics are such that any Democrat hoping to do well there must take positions that look Republican almost anywhere else. (Tomblin is antiabortion, though he controversially vetoed a bill to ban abortion after 20 weeks.)

Democrats appear to have pinned their hopes on a billionaire, Jim Justice, who joined the Democratic Party days before announcing his run. In a move that echoes Trump's pitch to voters, Justice is campaigning as an outsider who won't be influenced by special interests. A recent MetroNews West Virginia Poll  suggests that might be working. The poll shows Justice besting former U.S. attorney Booth Goodwin and state Sen. Jeff Kessler in the Democratic primary, but with 21 percent of likely primary voters still undecided. It also shows Justice in a 10-point lead over the lone Republican in the race, state Sen. Bill Cole. (Though general election matchups are hard to accurately pin down this early.)

1. Missouri (D): Democratic Gov. Jay Nixon is term-limited as well. To counter Missouri Republicans' success at the state level, Democrats are turning to state Attorney General Chris Koster, a former Republican, to keep the mansion in Democratic hands. They're aided by a crowded and chaotic primary on the Republican side. State Auditor Tom Schweich launched a campaign, then a month later committed suicide. There are now four GOP candidates, all of them viable: Lt. Gov. Peter Kinder, former state House speaker Catherine Hanaway, former Navy SEAL Eric Greitens, and businessman and former Senate candidate John Brunner. Each has their own advantage, whether it be money or resume, but Kinder is the best-known. Missouri voters are famously tough to pin down, though. That makes Missouri's governor's race a toss-up in a state that, notably, has voted for the Republican candidate for president since 2000.