"They're a joke. They're a laughingstock," Trump told reporters outside of the White House, when asked whether he would agree to debate three Republican challengers during the 2020 nominating contest.
In a tweet on Monday, Trump dismissed the three challengers as "the Three Stooges" and expressed doubt about ever agreeing to meet them on a debate stage.
Three Republicans - former U.S. Representative Mark Sanford of South Carolina, former Massachusetts Governor William Weld and former U.S. Representative Joe Walsh of Illinois - are mounting long-shot campaigns to deny Trump the 2020 Republican presidential nomination.
Trump also denied having anything to do with the cancellation of Republican primary contests in four states, meaning he will face no opposition there. Canceling their primaries were Nevada and South Carolina, which are critical early voting states, as well as Kansas and Arizona.
"The four states that canceled it don't want to waste their money. If there was a race, they would certainly want to do that," Trump told reporters on the South Lawn of the White House.