WASHINGTON (NewsNation Now) — In a reversal, Republican Sen. Bill Cassidy of Louisiana joined Democrats in voting against ending former President Donald Trump’s impeachment trial Tuesday.

Cassidy was among six Republican senators who sided with all Democrats on the question of whether a former president can be tried after leaving office. The Louisiana senator’s position was a switch from January, when he voted to end the proceedings on the grounds that they were unconstitutional.

“I took an oath to be an impartial juror and I took an oath to uphold and defend the Constitution of the United States,” Cassidy told NewsNation’s Joe Khalil. “If somebody — impartially, I can judge — they make the compelling argument that it is constitutional and the other side basically concedes, then pursuant to both oaths, I vote as I voted.”

The vote drew criticism from Republicans in the senator’s conservative state. Cassidy said he wasn’t surprised by some of the backlash he’s received, but added he has also received thank yous.

“When you properly understand it, that supporting the Constitution over an individual, people say ‘I get it,'” said Cassidy. “If any constitutional conservative disagrees with me, I’d like to hear why.”

When asked if he was open to convicting former President Donald Trump, Cassidy said he will continue to listen to the evidence as it is presented.

“I have not yet decided on how I will vote,” he said.

Republican Sens. Mitt Romney of Utah, Ben Sasse of Nebraska, Susan Collins of Maine, Lisa Murkowski of Alaska and Pat Toomey of Pennsylvania all joined Sen. Cassidy in voting against ending the trial on the basis of constitutionality.