WASHINGTON – The race for the United States Senate is heating up as battleground states are determined in an election cycle influenced by President Donald Trump’s job approval rating.

Four Republicans and one Democrat senator will not seek re-election for various reasons, from declining health to inability to work with a president they view as divisive, to a sexual harassment allegations that broke out of the Me Too movement. Here are some elections to watch:

Heidi Heitkamp, N.D. – D, and Jon Tester, Mont. – D, face uphill battles in states where Trump won the 2016 election with 63 percent and 55.6 percent of the vote respectively. Democrats could lose another seat in West Virginia as Joe Manchin, W.Va. – D, is up for re-election in a state Trump won with 67.9 percent of the vote.

Republicans could lose their seat in Arizona. Sen. Jeff Flake, Ariz. – R, will not seek re-election in a state where Trump won by only 48.1 percent of the vote. According to a Gallup poll conducted in January, 53 percent of Arizona residents surveyed disapprove of the current president’s job.

In order for the Senate to flip from red to blue, Democrats will need to maintain control over the seats they have now, and gain two seats currently held by Republicans.

As of last week, Trump’s national approval rating increased to 42 percent, the highest it’s been since May 2017 according to Gallup.

Explore the interactive map below to learn more about the 2018 midterm Senate race.