What are the races to watch?
Top Democratic targets include Maine and Colorado, the only two states Trump lost in 2016 where Republicans are defending Senate seats in 2020.
Sen. Susan Collins, a politically dominant figure in Maine for a generation, is seeking a fifth term, while Sen. Cory Gardner is running for his second. The Democratic Senatorial Campaign Committee, the campaign arm of Senate Democrats, endorsed Maine House Speaker Sara Gideon against Collins and former Colorado Gov. John Hickenlooper against Gardner.
The DSCC also has preferred candidates against Republican incumbents in states that backed Trump by modest margins in 2016. The group is backing gun control activist and former astronaut Mark Kelly against Sen. Martha McSally in Arizona, former state Sen. Cal Cunningham against Sen. Thom Tillis in North Carolina, businesswoman Theresa Greenfield against Sen. Joni Ernst in Iowa, and Air Force veteran MJ Hegar against Sen. John Cornyn in Texas. Arizona and North Carolina may be more competitive than Iowa and Texas.
Georgia, where Trump won by 5 points in 2016, is hosting two Senate elections in 2020: Republican Sen. David Perdue is seeking a second term and Sen. Kelly Loeffler is running in a special election after being appointed in January to succeed Republican Sen. Johnny Isakson.
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Most of the rest of the Republican seats at stake in 2020 are probably out of reach for the Democrats. In 15 of the 23 contests where Republicans have Senate seats on the ballot, Trump carried those states in 2016 by at least 14 percentage points.
Some are worth watching, though. They include Kansas, where Pat Roberts is retiring and the Democrats would have an opening if former Kansas Secretary of State Kris Kobach won the Republican primary. In Kentucky, Majority Leader Mitch McConnell has a big-spending Democratic opponent in Amy McGrath, a former military pilot who almost won a very pro-Trump district in 2018.