As President Donald Trump’s impeachment trial shifted to its question-and-answer phase, Republican Sen. Susan Collins of Maine started off by asking Trump’s attorneys about the president’s motives.

The senator’s question was read as follows by Chief Justice John Roberts: “If President Trump had more than one motive for his alleged conduct — such as the pursuit of personal political advantage, rooting out corruption, and the promotion of national interest — how should the Senate consider more than one motive in its assessment of Article 1?”

The first article of impeachment charges Trump with abuse of power.

Patrick Philbin, one of the president’s lawyers, responded to the query from Collins. She said she was asking the question on behalf of herself and Sen. Lisa Murkowski of Alaska and Sen. Mitt Romney of Utah, two other Republican lawmakers viewed as key swing votes in the trial.

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“If there is something that shows a possible public interest and the president could have that possible public-interest motive, that destroys their case. Once you’re into mixed-motive land, it’s clear that their case fails,” Philbin said.

The Democrats’ push to remove Trump from office centers on his pressure on Ukraine’s president to announce investigations into Biden and his son, as well as into an unsubstantiated theory that Ukraine interfered in the 2016 presidential election.

Trump, charged with both abuse of power and obstructing Congress, is only the third American president to have been impeached, joining Andrew Johnson and Bill Clinton.

However, impeachment by the House doesn’t mean removal from office. Neither Johnson nor Clinton was found guilty in impeachment trials in the Senate, and the same outcome is widely expected in the impeachment of Trump, whose Republican Party occupies 53 of the chamber’s 100 seats. That helps explain why the stock market DJIA, +0.64% SPX, +0.53% hasn’t reacted much to impeachment-related developments.

A two-thirds majority of the Senate — or 67 senators — must vote to convict the president to remove him from office.

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And read: Why investors are so calm about impeachment — and what it would take for that to change