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“Hopefully he won’t do that again.”

That’s what Senator Lamar Alexander told me on Friday, discussing President Donald Trump’s push to have political rivals investigated by Ukraine. A lot of weight rests on those six words, especially the first. The veteran lawmaker would like the president not to abuse his power, and is relying on the political system to check him, even though Alexander does not think it is right to apply the most powerful check Congress has.

The Republican from Tennessee had been seen as an essential vote if the Senate was to call witnesses in the president’s trial. Last week he said he needed no testimony, because the House had already proved its case: “If you’ve got eight witnesses saying that you left the scene of an accident, you don’t need nine.” Alexander said he was equally certain that the president’s offenses do not merit removal. “You don’t apply capital punishment to every offense,” he said.

What is a proper response by Republicans who do not accept the president’s view that his conduct was “perfect”? How can Congress make sure “he won’t do that again”? “I think it’s appropriate for me as a United States senator to say, ‘Mr. President, you shouldn’t do that,’” Alexander told me. This sounds mild compared with the impassioned speeches by Representative Adam Schiff, leader of the prosecution. But Alexander stands as one of relatively few Republicans willing to publicly say a critical word about the president. In Alexander’s case, the word is inappropriate, his description of the acts for which the president was impeached. “I agree that he called the president of Ukraine and asked him to investigate the Bidens,” he said, and “I was convinced that at least in part, he withheld [military] aid in order to encourage the investigation.”

Alexander’s statement does not change his vote for acquittal. “As a practical matter, it makes no difference at all,” my colleague Mara Liasson said on NPR Sunday. But in the slightly longer term, she said, his statement could matter because “the Senate is sending a message” through this proceeding. The president can be told to change his behavior, or be told that Congress will do nothing to constrain him.

Alexander would like other Republicans to adopt his stance, and on Sunday, one tried. Senator Joni Ernst once declared in a campaign ad, “I grew up castrating hogs on an Iowa farm,” and promised to make Washington’s big spenders “squeal.” She was more restrained on CNN’s State of the Union with Jake Tapper:

Ernst: The president has a lot of latitude to do what he wants to do. Again, not what I have done, but certainly, again, going after corruption, Jake ... Maybe not the perfect call.

Tapper:  If it’s not something you would have done, why wouldn’t you have done it? Because it was wrong? Because it was inappropriate?

Ernst:  I think, generally speaking, going after corruption would be the right thing to do.

Tapper:  No, but going after the Bidens.

Ernst:  He did it—he did it maybe in the wrong manner … But I think he could have done it through different channels.

Republicans know that their base voters still overwhelmingly back the president, though many deny that this influences their measured comments. “I’m not terrified by him,” Alexander told me. “I say what I think.” The 79-year-old, who is not seeking reelection, says Congress still has leverage over the president.

I asked if the president’s acquittal will free him to repeat the very acts Alexander calls inappropriate. “He could,” Alexander conceded, but “I would think that the fact that he’s had to endure an impeachment process would be something for him to think about. I think the fact that he’s about to run for reelection and present himself to all the American people and try to get a majority of votes would be something to think about. I think the fact that he has appropriations bills, which we have to vote on; the War Powers Act, which we have to vote on; his decision to take money and use it to build a wall in a way that’s not authorized, which we have to vote on—all those are checks and balances.”

It’s true that the president still needs Congress to pass spending bills and help support his reelection; this gives him incentive to listen to lawmakers’ private counsel. But it is also revealing that when Alexander listed some of the issues on which Congress may have leverage, they include several items on which the president is already accused of usurping the authority of Congress—such as diverting money to pay for a wall and, for that matter, withholding congressionally mandated military aid to Ukraine.

It is also true that the president seems to have lost the public debate over soliciting foreign help in an election; majorities of voters have told pollsters it is wrong. This would seem to be a powerful signal to an official facing voters in November. But Trump maintains the backing of Republican voters and even the support of Alexander. “I’m honorary chairman of his campaign in Tennessee,” he said, citing the strong economy and the appointment of conservative judges.

Before the House voted to impeach the president, I sat with Schiff and asked what would happen if lawmakers failed to remove Trump. “I’ve always thought that the strongest argument for impeachment was also the strongest argument against it,” Schiff conceded. Failing to impeach the president, he said, would signal that his conduct was acceptable. But impeaching the president and failing to remove him could send an identical signal.

If senators vote as expected on Wednesday, the president will have an opportunity, if he wishes, to read his acquittal as “complete and total exoneration”—the phrase he used about Robert Mueller’s report, which compiled much evidence of wrongdoing without recommending specific action against the president. If any different meaning is to be assigned to the impeachment verdict, it will be up to the senators who vote on it.

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