“The Founders entrusted our elections chiefly to the states — not Congress," Cotton said. "They entrusted the election of our president to the people, acting through the Electoral College — not Congress."

Trump also lobbed a more general attack at Republicans who have disavowed the effort — a group that includes former House Speaker Paul Ryan, who said it is "difficult to conceive of a more anti-democratic and anti-conservative act."

“The ‘Surrender Caucus’ within the Republican Party will go down in infamy as weak and ineffective ‘guardians’ of our Nation, who were willing to accept the certification of fraudulent presidential numbers!” the outgoing president tweeted.

The Arkansas Republican has been floated as a future presidential candidate, and the Electoral College challenge has divided the GOP at a time when it is trying to maintain its grip on the Senate majority.

Two incumbent Georgia Republicans, Sens. David Perdue and Kelly Loeffler, are hoping to fend off Democratic challengers in a runoff Tuesday. Both have aligned themselves closely with the president, who is scheduled to hold a rally on their behalf in Georgia later Monday. The president also recently asked Georgia Secretary of State Brad Reffensperger during a private phone call to "find" enough votes to overturn Biden's victory in the state. A recording of the call was subsequently leaked to the media.

Trump has actively encouraged the Electoral College challenge and shortly after his warning shot at Cotton, the president tweeted quotes from Sens. Ted Cruz (R-Texas.) and Ron Johnson (R-Wis.) — both of whom support the effort.

Johnson defended the bid to reverse Biden’s electoral victory, arguing that Republicans cannot ignore the “legitimate concerns” about unsubstantiated allegations of widespread voter fraud put forth by Trump and his allies.

“From my standpoint, we simply cannot dismiss the concerns of tens of millions of Americans that have suspicions,” Johnson said Monday on Fox News. “What we're saying is let's delay accepting a particular state's electors until we actually investigate what the issues are in that particular state.”