Former South Carolina Rep. Mark Sanford Mark SanfordOn The Money: Business world braces for blue sweep | Federal Reserve chief to outline plans for inflation, economy | Meadows 'not optimistic' about stalemate on coronavirus deal Trump critic Sanford forms anti-debt advocacy group Republicans officially renominate Trump for president MORE, a Republican challenging 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 in a longshot primary campaign, said on Sunday that he isn't sure if he would still consider voting for Trump in 2020, despite allegations that the president solicited foreign interference to benefit him politically.

Host Jake Tapper Jacob (Jake) Paul TapperThe media's misleading use of COVID-19 data Julia Louis-Dreyfus: 'We can't spend much time grieving' Ginsburg Pence aide dismisses concerns rushed vote on Trump nominee will hurt vulnerable senators MORE asked Sanford on CNN's "State of the Union" if he would vote for Trump over 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 if they end up being the candidates in 2020.

"I don’t know," Sanford responded. "What I've said is I'm an issue guy." ADVERTISEMENT

Sanford said he's going to base his decision on "who is going to be closest to me" with a focus on debt and spending.

Former Illinois Rep. Joe Walsh Joe WalshSunday shows preview: Protests continue over shooting of Blake; coronavirus legislation talks remain at impasse Republicans officially renominate Trump for president Tucker Carlson responds to guest correcting pronunciation of Kamala Harris's name: 'So what?' MORE, a fellow 2020 GOP challenger, said there is "no way in hell" he would vote for Trump.

"I'm running against President Trump because he's unfit," Walsh said.

"The debate is about Trump, period," he added.

The Republicans were also split on where they stand on impeachment, with Walsh saying the president deserves to be impeached based on his public actions alone and Sanford saying Congress needs to follow a formal investigation process.

Trump is facing an impeachment inquiry after a whistleblower came forward with allegations that Trump asked Ukraine to investigate Biden and his son.

A partial memo of a call between Trump and Ukrainian President Volodymyr Zelensky shows Trump asking the foreign leader to investigate the Bidens.

Trump publicly called on China and Ukraine to investigate the Bidens when speaking to reporters last week.