The three 2020 Democrats Trump's campaign is watching most closely

The reelection campaign has begun compiling opposition research on Kamala Harris, Elizabeth Warren and Cory Booker and is eyeing opportunities to attack them. The effort began over the weekend when the Trump campaign sent out a news release ahead of Warren’s launch criticizing her past claims of Native American heritage…

Trump has told allies he sees Biden, who remains undecided on a 2020 bid, as the most formidable potential general election rival. The president has said privately that Biden would appeal to a wider swath of voters than other Democratic hopefuls.

Yet among the president’s inner circle, there’s widespread doubt that Biden could survive a primary, after a three-decade political career and positions on issues such as the Iraq war and crime that are anathema to liberals. Many are convinced that whoever emerges from the Democratic primary will be an out-of-the-mainstream liberal — someone who either hails from that wing of the party or has taken pains to align themselves with it.