Former U.S. President Donald Trump's second impeachment trial of  is set to unfurl Tuesday with some of the important questions about the proceeding itself still up in the air, according to CNN.

Top Republican senators at the weekend continued to contend that Trump's Senate impeachment trial is constitutionally illegal.

Despite a brief period of doubt about whether to impeach the former commander in chief, Republicans are bent on presenting a united front in junking the case that a U.S. Senate trial must convict Trump for inciting the Jan. 6 Capitol siege.

Five people were killed in the riots at the U.S. Capitol, including a police officer.

"If being held responsible means being impeached by the House and convicted by the Senate, the answer to that is no," Republican Sen. Roger Wicker of Mississippi said in remarks quoted by the Associated Press.

With Democrats already highlighting Trump's culpability, MSNBC's legal expert Danny Cevallos compared impeachment manager Jamie Raskin's request for Trump to appear as a witness at the Senate trial as a "constitutional jiu jitsu" trap.

House Democrats have sought testimony from Trump at the impeachment trial, a move that was quickly opposed by Trump's lawyers. It would be "a farce, unwise and with "zero chance of conviction," says Republican Sen. Rand Paul of Kentucky.

Trump's legal team has asserted that it's unconstitutional to carry out an impeachment trial for a private citizen. However, many legal luminaries believe that such a trial is constitutionally legitimate

For his part, Republican Sen. Lindsey Graham of South Carolina, one of Trump's avid backers, believes the former president's behavior was unjust and "he's going to have a place in history for all of this," AP said. 

Meanwhile, Republicans who supported the push to impeach Trump now face a critical reaction from their constituents as the issue continues to split up the party.