Berkeley law professor John Yoo warns that impeaching Donald Trump over his alleged solicitation of re-election assistance from Ukrainian President Volodymyr Zelenskiy could undermine presidential powers to conduct foreign policy and protect national security. Given Yoo's expansive understanding of those powers, that prospect may count as an argument in favor of impeachment.

"The Constitution vests the president with the authority to conduct foreign policy and the responsibility to protect the nation's security," Yoo writes in a New York Times op-ed piece. "A president, even one who is possibly engaging in wrongdoing, must have confidence in the confidentiality of his communications or he will be unable to perform his constitutional duties and our international relations will fall victim to government by committee."

Yoo worries that "if Congress could regulate presidential discussions with foreign leaders, presidents and foreign leaders would speak less candidly or stop making the calls altogether." If that happened, he says, "United States foreign policy—approved by the American people at each election—would be crippled."

But is Congress trying to "regulate presidential discussions with foreign leaders," or is it investigating a possible abuse of presidential power, including an illegal usurpation of the legislative branch's spending authority? If Trump put a hold on congressionally approved military aid with the intent of pressuring the Ukrainian government to dig up politically useful dirt on former Vice President Joe Biden, George Mason law professor Ilya Somin notes, he violated the separation of powers.

It would not be the first time. Yoo himself has criticized Trump for overstepping his constitutional authority by trying to build a border wall that Congress has refused to fund, by suggesting he might pay for the wall by imposing tariffs on Mexico, and by threatening to unilaterally withdraw from the North American Free Trade Agreement.

"The framers believed that 'high crimes and misdemeanors' included a president who used his foreign affairs powers for personal or political gain," Yoo concedes. To investigate whether Trump has done that, he says, "A special congressional committee could review classified information in secret and bring United States and foreign officials to testify under oath. The House could meet any stonewalling by cutting intelligence, military and diplomatic funding."

And then what? If Congress confirms that Trump has in fact "used his foreign affairs powers for personal or political gain," that would be an impeachable offense, according to Yoo. Yet he resists the logical conclusion that an impeachable offense should result in impeachment.

"The founders believed that impeachment should come only as a last resort," Yoo says. But the quote he uses to back up that claim suggests nothing of the sort: "At the end of four years, the president may be turned out of his office, Gov. Edmund Randolph said in 1788 as Virginia weighed ratifying the Constitution. 'If he misbehaves he may be impeached, and in this case he will never be re-elected.'" That hardly means Congress has to wait for the next election instead of trying to remove a president who has committed an impeachable offense.

"Democratic presidential candidates are calling for impeachment," Yoo writes. "But they should realize that they themselves remain the framers' primary remedy for presidential abuses of power. The Constitution trusts the American people, acting through the ballot box, to render judgment on President Trump. Democrats should trust the framers' faith in the American people, too."

While there may be sound political reasons to choose the course that Yoo recommends, there are also sound constitutional reasons not to simply let voters decide Trump's fate. Even if an impeachment vote does not result in conviction by the Republican-controlled Senate (as seems pretty certain at this point), it would make a statement about limits on presidential power that even Yoo acknowledges. If the discovery of impeachable offenses is not a good reason to impeach a president, what is the point of the impeachment power?