Leading Republicans took to the talk show circuit Sunday to defend their expected acquittal of U.S. President Donald Trump at his Senate trial next week – despite offering sharp criticism of his role in the Ukraine scandal. 

The president was impeached in December for abuse of power over pressuring ally Kiev to announce investigations that would have helped him politically, including into Joe Biden, a leading challenger in this year's presidential ballot. 

A day ahead of the Iowa Democratic caucuses – the official start of the election season – key Republican senators including Lamar Alexander and Joni Ernst said Trump's behavior was troubling but did not warrant removal. 

"Hopefully, he'll look at this and say, 'Okay, that was a mistake. I shouldn't have done that, shouldn't have done it that way,'" Alexander told NBC.

The Tennessee senator suggested Trump had been naive in asking a foreign ally to look into Biden and his son Hunter's business dealings in Ukraine, which Republicans have claimed without evidence were corrupt. 

But he added: "The bottom line: it's not an excuse. He shouldn't have done it."

Trump is all but assured of being acquitted at only the third impeachment trial of a U.S. president, with Republicans holding 53 seats in the Senate to 47 for the Democrats. A two-thirds majority, or 67 senators, is needed to remove him from office. 

Ernst said it was "up to the American people" to decide on Trump's behavior, adding that she would vote Wednesday to acquit the president, who is also accused of obstruction of Congress. 

"I think generally speaking, going after corruption is the right thing to do, but he did it in the wrong manner… I think that he could have done it in different channels," she told CNN.

A narrow majority of Americans believe Trump abused his power and obstructed Congress by withholding documents and testimony during the impeachment inquiry, according to a new NBC/WSJ poll. 

But they remain divided on whether he should be kicked from office, with 46 percent hoping to see him removed and 49 percent saying he should keep his job. 

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Democratic pollster Cornell Belcher suggested Trump's conduct had forced House Speaker Nancy Pelosi's hand when she would rather not have started impeachment proceedings. 

"Nine million more people voted for Democrats last time around than Republicans. We have winning messages without impeachment," he told NBC.

On Friday, Democrats failed to muster the four Republican votes needed to allow witness testimony – a departure from every other impeachment trial in U.S. history. 

They had been eager to hear from Trump's former national security advisor John Bolton, acting White House chief of staff Mick Mulvaney and other key administration figures caught up in the scandal. 

Bolton reportedly says in a forthcoming book Trump told him military aid to Ukraine was tied to Kiev's investigating Biden – corroborating the central claim against the president. 

Alexander said, however, there was no need for more evidence and, with Washington awaiting the results of Monday's Iowa caucuses, it was better to let the American public decide who should be the next president. 

The first vote in the U.S. primary process will be closely watched as a sign as to which of 11 Democratic candidates are gaining early momentum to challenge Trump in November's election. 

"As upsetting as what's going on in the Senate is, the thing that I'm always reminding voters of – especially in these closing days of the Iowa caucuses – is that, yes, the Senate is the jury today but we are the jury tomorrow," Pete Buttigieg, who is running third in the Hawkeye State, told CNN. 

"And we get to send a message at the ballot box that cheating, lying, involving a foreign country in our own domestic politics, not to mention abuse of power more broadly and bad administration, that that's not okay, that we can do better."

The Senate resumes as a court of impeachment on Monday to hear final arguments, before voting on Wednesday on the two articles of impeachment passed last month in the House. 

Adam Schiff, the leader of the House impeachment managers, told CBS Sunday that it was "pretty remarkable" that senators on both sides had acknowledged that Democrats had proved their case against the president. 

"But I'm not letting the senators off the hook. We're still going to go into the Senate this week and make the case why this president needs to be removed. It will be up to the senators to make that final judgment, and the senators will be held accountable for it." 

Four contenders for the Democratic nomination – Bernie Sanders, Elizabeth Warren, Amy Klobuchar and Michael Bennet – were required to be present at the impeachment trial. 

Monday's Iowa vote is headed to a photo finish, with leftist Bernie Sanders holding a narrow polling lead over Biden. 

(Cover: U.S. President Donald Trump rallies with supporters in Des Moines, Iowa, U.S., January 30, 2020. /Reuters Photo)