Sen. Lamar Alexander (R-Tenn.) said on NBC's "Meet the Press" that he believes President Trump withheld military aid to Ukraine to "encourage" its government to investigate the Bidens, but that he will vote to acquit Trump on Wednesday because he believes the consequences of the president's actions should be decided in the next election.

Why it matters: Alexander, who is retiring at the end of his term and thus doesn't have to worry about re-election pressure, was viewed as a possible Republican swing vote in last week's vote to call witnesses in the impeachment trial. He and moderate Sen. Lisa Murkowski voted against the motion, essentially ensuring Trump's swift acquittal.

"If you have eight witnesses who say someone left the scene of an accident, why do you need nine? I mean, the question for me was: Do I need more evidence to conclude that the president did what he did? And I concluded no."

— Sen. Lamar Alexander to NBC's Chuck Todd

What he's saying: Alexander said he believes Trump should not have withheld military assistance from Ukraine or asked Ukraine's President Volodymyr Zelensky to announce an investigation into Joe and Hunter Biden.

"I think he shouldn't have done it. I think it was wrong. Inappropriate was the way I'd say — improper, crossing the line," he said. "I think what he did is a long way from treason, bribery, high crimes and misdemeanors."

Alexander said Trump should have taken his concerns about corruption in Ukraine to the Department of Justice rather than asking the country directly. When asked why he did not go to DOJ, Alexander said, "Maybe he didn't know to do it."

Pressed on whether an acquittal would embolden Trump to continue to solicit foreign election interference, Alexander responded: "I hope not."

"I mean, enduring an impeachment is something that nobody should like," Alexander said. "Even the president said he didn't want that on his resume. I don't blame him. So if a call like that gets you an impeachment, I would think he would think twice before he did it again."

The other side: Lead House impeachment manager Adam Schiff (D-Calif.) said on CBS' "Face the Nation" that it's "remarkable" that Republican senators are saying that the House proved its case.

He disagreed that the election should decide the consequences of Trump's actions, arguing that the president is "threatening to still cheat" in November by soliciting foreign interference.

"To call solicitation, coercion, blackmail of a foreign power, an ally at war, by withholding military aid to get help in cheating in the next election merely inappropriate, doesn't begin to do justice to the gravity of this president's misconduct," Schiff added.

The big picture: Alexander said the voters in the 2020 election have a right to decide if Trump's actions were wrong and that removing Trump could establish a "perpetual impeachment" on partisan lines that would "immobilize" the Senate and the presidency.

A majority of Americans believe Trump abused his power and obstructed Congress in the impeachment inquiry, according to an NBC/WSJ poll.

Just 46%, however, believe that he should be removed from office.

Go deeper: The daily highlights from Trump's Senate impeachment trial