However many governor's races Dems win, they'll only be chipping away at GOP's historic level of success

Just as in the battle for the House, Democrats are almost certain to pick up governor's mansions this November. The most competitive races keep tilting their way.

Nine of the 10 races most likely to flip parties are held by Republicans, spanning the country from Iowa to New Mexico. And while none makes our top 10, open seats in traditionally conservative states, such as Georgia, Kansas, South Dakota and Oklahoma, are all competitive.

The catch is that however many governor's races the Democrats win, they will only be chipping away at Republicans' historic level of success. Republicans control 33 governor's mansions, a near-record high, and those include blue and swing states. And it's not impossible that Republicans might also pick up control of a state like Connecticut, though that one has fallen off our top 10 list.

Democratic gubernatorial victories are critical for the future of the party. Many of the winning governors will have strong influence over the legislative districts drawn after new census data is released in 2020. Democrats, far behind in control of state legislatures and governor's mansions, need to start picking up all the seats they can this year to keep from being locked out of the map-drawing process for Congress and state legislatures two election cycles from now.

Here are our latest rankings of the 10 governor's races most likely to flip parties, ranked in order of least likely to flip (10) to most (1).

10. Ohio (Republican-held seat that will be open in 2018. Previous ranking 9)

With Gov. John Kasich, R, term-limited, Democrats are trying to take a seat in a state that Donald Trump won by 10 points in 2016. They've nominated a liberal hero of sorts in former Consumer Financial Protection Bureau chief Richard Cordray. But GOP candidate Mike DeWine, a former U.S. senator and the state's current attorney general, has fairly strong name identification. And anti-Trump, anti-Republican sentiment in the state doesn't appear to be manifesting quite as Democrats had hoped: Trump's approval rating hovers just below 50 percent. This race moves slightly less likely to flip to Democrats.

9. Iowa (Republican-held. No previous ranking)

Both sides say this is a real race. Gov. Kim Reynolds, R, was elevated to the job last year after Terry Branstad was appointed ambassador to China, so she doesn't quite have the power of incumbency. Trump's tariff war with China doesn't seem to be playing well with Iowa farmers, either, as some operatives say his popularity in the state has slipped dramatically. Two public polls in September put Democrat Fred Hubbell, a wealthy businessman, with a slight edge or within the margin of error.

8. Wisconsin (Republican-held. Previous ranking 10)

One of the hardest things to do in politics is knock off a sitting governor, especially one as well-established as Gov. Scott Walker, R, who is going for a third term. But recent public and private polling show his Democratic challenger, Tony Evers, has a good chance. Democrats won some big special and statewide elections this year. Will the small slice of truly independent voters in Wisconsin tire of Republican control and want a change, or do they stick with the governor they've had since 2011?

7. Florida (Republican-held open seat in 2018. No change in ranking.)

One Republican operative described Florida as the purest toss-up race in 2018. And it looks that way, as conservative Rep. Ron DeSantis battles it out with liberal Democrat Andrew Gillum in a clash of personalities and policies. After starting out with a lead, recent polling shows Gillum up but just by a point or two, though Democrats say they think the race is trending their way. The question is what do suburban swing voters dislike more: DeSantis's wholehearted embrace of Trump or Gillum's proposals for single-payer health care and for ending the Immigration and Customs Enforcement agency?

6. Nevada (Republican-held open seat in 2018. No change in ranking.)

Nevada Democrats are trying to keep their up- and down-ballot success in 2016 going by taking the governor's mansion from term-limited Brian Sandoval, R) who is leaving office with some 60 percent of the state feeling as if Nevada is on the right track. It helps Democrats that Sandoval hasn't endorsed the Republican nominee, Attorney General Adam Laxalt. Meanwhile Democratic nominee Steve Sisolak, a commissioner of the county that includes Las Vegas, is running ads tying himself to Sandoval's education policy. A recent NBC News/Marist poll shows the race as a dead heat. Is that enough for Laxalt in a state that's trending Democratic?

5. Maine (Republican-held open seat in 2018. Previous ranking 4)

If there's any race where the battle over Brett Kavanaugh could alter the dynamic, it's this one. Will Sen. Susan Collins', R-Maine, decisive vote to put him on the Supreme Court drive voters toward Democratic Maine Attorney General Janet Mills? Some private polling suggests independents could be leaning toward Mills. But Republicans nominated businessman Shawn Moody, who has plenty of money to try to outrun unpopular outgoing GOP Gov. Paul LePage's large shadow. This race remains close and especially unpredictable, with two third-party candidates in the mix.

4. Michigan (Republican-held seat that will be open in 2018. Previous ranking 5)

The race to replace outgoing, unpopular GOP Gov. Rick Snyder keeps looking rosier for Democrats. They say Gretchen Whitmer, the former party leader in the state Senate, is one of the smartest campaigners of all of 2018 with a simple "Fix the Damn Roads" slogan. She's buoyed by Democratic activists who are frustrated that their state went for Trump in 2016 and don't want to be caught sleeping again. In addition, Republican Attorney General Bill Schuette just doesn't seem to have caught on as a candidate.

3. New Mexico (Republican-held seat open in 2018. Previous ranking 1.)

Neither side is particularly enthusiastic with the way their candidate - Democratic Rep. Michelle Lujan Grisham and Republican Rep. Stevan Pearce - has panned out. This state is challenging for Republicans to hold onto for so many reasons: It's a majority-Hispanic state, it's trending blue (Hillary Clinton won it by 10 points), and outgoing Republican Gov. Susana Martinez is one of the most unpopular governors in America. Still, it moves back a few spots to make room for our top two races most likely to flip parties.

2. Alaska (Independent-held. Previous ranking 3)

Gov. Bill Walker, I, is having a tough time trying to win reelection in a state with high unemployment. He has two challengers, Republican Mike Dunleavy and Democrat Mark Begich. Polling shows Dunleavy leading by double digits. "Alaska is still a red, Republican state, and this is a course correction," said one confident GOP operative.

1. Illinois (Republican-held. Previous ranking 2)

Illinois Gov. Bill Rauner, R, is the most vulnerable governor this cycle. Despite having endless millions to spend on his race, he was always going to have a tough path to reelection in a Democratic state. It was the entrance of a third-party conservative candidate that appeared to seal his fate by making Rauner a governor without a natural constituency. Democrat J.B. Pritzker, another billionaire, looks as if he'll cruise to victory.