WASHINGTON (CNN) The sitting Senators in two of the most closely watched re-election fights this fall are running nearly even with their challengers, according to new CNN polls conducted by SSRS.

Democratic Sen. Claire McCaskill edges challenger Josh Hawley 47% to 44% among likely voters in Republican-friendly Missouri, while Republican Sen. Dean Heller stands four points behind his Democratic challenger Jacky Rosen in Nevada (47% Rosen to 43% for Heller), which has broken for Democrats in each of the last three presidential contests and has been a regular Senate battleground in the last decade.

Related: Full poll results for Missouri and for Nevada

In both states, the political equilibrium has been shifting away from the party of the incumbent senator up for reelection this year. Missouri is one of several states where Democratic Senators are on defense in deep-red territory, a playing field that could be a bright spot for the GOP even while control of the House of Representatives is squarely in play. Nevada is widely seen as Democrats' best Senate pickup opportunity.

President Donald Trump's approval rating among likely voters is a mirror image in these two states, illustrating the political challenge facing each Senator. While 51% of Missouri likely voters approve of Trump's performance, an equal 51% of Nevada likely voters disapprove of the way the President is handling his job.

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