Five Senate Democrats would lose to Republican candidates if the elections were held today and three have approval ratings under 50%, according to new Axios/SurveyMonkey polls.

Expand chart Data: SurveyMonkey polls conducted February 12-March 5, 2018. Poll Methodology; Chart: Andrew Witherspoon / Axios

Why it matters: Democrats are defending 10 Senate seats in states that President Trump won in 2016. In six of those states, Trump's approval is higher than 50% (compared to 43% nationally). These numbers underscore how hard it will be for Democrats to pick up the two seats needed to win the majority despite Trump’s troubles.

The most vulnerable senators are Joe Manchin of West Virginia, Jon Tester in Montana and Claire McCaskill in Missouri. Each of their approval ratings is either under 50% or just above it, while Trump's is well above that in all three states.

The least vulnerable senators are Bill Nelson of Florida, Bob Casey of Pennsylvania, and Sherrod Brown of Ohio. Trump's approval is at just 46% in Florida and Pennsylvania and 54% in Ohio.

But, but, but... With the election many months away and final Republican opponents not set, these numbers are likely to change as real GOP challengers get involved in the race. The approval ratings of each senator may give a better idea of where they stand with voters in their states.

By the numbers:

Trump’s approval is higher than the incumbent senators in six states (WV, ND, MT, IN, MO, OH). It’s higher than his national approval rating in all 10 states.

North Dakota voted for Trump over Hillary Clinton by a 36 point margin, but a generic Republican candidate would have just a 2 point lead over Sen. Heidi Heitkamp.

Wisconsin Sen. Tammy Baldwin's narrow three-point advantage over a generic Republican candidate is underscored by outside conservative groups that have already spent millions of dollars in attack ads against her.

Sen. Casey in Pennsylvania is polling nine points ahead of his GOP challenger Lou Barletta, whom Trump has already publicly endorsed (though the president's approval rating in the state is 46%).

Stay tuned: We'll be polling next some of the GOP seats that are in play such as Arizona, Nevada and Tennessee.

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Methodology: These SurveyMonkey/Axios online polls were conducted February 12- March 5, 2018 among a total sample of 17,289 registered voters living in Florida, Pennsylvania, Ohio, Michigan, Wisconsin, Missouri, Indiana, West Virginia, Montana, North Dakota.