Republican strategist Lauren Claffey told Hill.TV on Wednesday that former Vice President Joe Biden Joe BidenFormer Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick Bloomberg rolls out M ad buy to boost Biden in Florida MORE and Sen. Bernie Sanders Bernie SandersSirota reacts to report of harassment, doxing by Harris supporters Republicans not immune to the malady that hobbled Democrats The Hill's Morning Report - Sponsored by Facebook - Republicans lawmakers rebuke Trump on election MORE (I-Vt.) posed the biggest threats to President Trump Donald John TrumpFederal prosecutor speaks out, says Barr 'has brought shame' on Justice Dept. Former Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick MORE out of the 2020 Democratic primary field.

"I think that's why you see the Trump campaign talking about Biden so much," Claffey, the managing director at Hamilton Place Strategies, told hosts Krystal Ball and Buck Sexton on "Rising."

"The problem with Biden is that he's going to appeal to the exact same voters that Trump was able to convert in those blue states, those Rust Belt states," she continued.

"[Trump is] looking to keep that stronghold of people that got him to election in 2016," she said.

"Everybody else is over talking about, you know, Medicare for All and 'Green New Deal' and voting rights for felons, and it's just all the way over here on the left, and he's not worried about those people appealing to his base of supporters," she said. "Biden, and a little bit of Bernie, I guess, would be the only threats for him in his reelection."

Trump has attacked Biden and Sanders in recent weeks, taking aim specifically at Biden since his formal entrance into the 2020 Democratic primary.

The president in an early morning Twitter spree on Wednesday highlighted support from rank-and-file firefighters after a top union's leadership backed Biden.

— Julia Manchester