Former South Carolina Rep. Mark Sanford accused conservatives of choosing "to ignore this mounting crisis out of fealty" to Trump.
The former South Carolina governor focused on the national debt in his campaign, calling Trump the "king of debt."
South Carolina is among at least four states that have nixed Republican primaries and caucuses, an effort that helps smooth Trump’s path to reelection.
"Warriors stand and fight for what they believe," wrote three of the president's Republican challengers.
The president called the Federal Reserve Board members "boneheads" as he pushed for a rate cut that would put money in his own pocket.
The president's attempted dig at Republican rival Mark Sanford got roasted on "Late Night."
"I’m not looking to give them any credibility," the president told reporters of his fellow Republicans Mark Sanford, Joe Walsh and Bill Weld.
The former South Carolina governor is the third Republican to announce a bid against President Donald Trump.
The South Carolinian said his bid would focus on the growing federal debt and deficit, issues he says are being largely ignored.
"This is a brazen effort to boost sales by the American Egg Board."