WASHINGTON — In January 1999, Sen. Charles Schumer, D-N.Y., voted against a resolution allowing witnesses to be subpoenaed during President Bill Clinton’s impeachment trial. A day later, he voted for an amendment offered by Sen. Tom Daschle, D.-S.D., to prohibit any further evidence, argument or deliberations except for two hours of concluding argument by each side. But now, as Senate minority leader, Schumer is singing a different tune. “If you want the truth, you have to have witnesses,” he insists. “Who has ever heard of a trial without witnesses and documents?” Be careful what you wish for, Senator. If the Democratic House managers can call witnesses, so can the president’s legal team. Democrats might soon find that Trump is not the only one on trial — former vice president Joe Biden will be as well.

If Democrats call former national security adviser John Bolton to testify, Republicans can call Hunter Biden. His testimony would be relevant, as George Washington University law professor Jonathan Turley recently pointed out, because part of Trump’s defense is that he raised Hunter Biden’s Ukrainian business dealings in his call with President Volodymyr Zelensky as part of a larger concern about corruption in Ukraine. If Hunter Biden’s contract with Burisma was corrupt, then Trump can argue raising it had a “public purpose.”

But Hunter Biden’s testimony might only be the beginning. The president’s legal team could also call former Obama administration officials who warned then-Vice President Biden about his son’s business dealings in Ukraine. For example, they could call former White House energy czar Amos Hochstein, who the New Yorker reports “raised the matter with Biden,” to testify under oath about the concerns he expressed to the vice president and how he responded. They could call Christopher Heinz, then-Secretary of State John Kerry’s stepson, who broke business ties with Hunter Biden over Burisma because “working with Burisma was unacceptable,” a spokesman said. They could call former State Department officials, such as then-Deputy Secretary Antony Blinken, who met with Hunter Biden during his time on Burisma’s board.

The president’s legal team could then call nonpartisan experts to testify that Hunter Biden’s contract was corrupt. For example, they could call Yoshiko M. Herrera, a political science professor at the University of Wisconsin-Madison, who has said that “if Biden is working for the Obama administration on Ukraine, his son should not have been on the board of a company there that could be affected by U.S. policy spearheaded by his father.” They could call Robert Weissman, president of the progressive watchdog Public Citizen, who said, “It’s hard to avoid the conclusion that Hunter’s foreign employers and partners were seeking to leverage Hunter’s relationship with Joe, either by seeking improper influence or to project access to him.” They could even call Turley, who has written that “the Biden contract was so openly corrupt it would have made Jack Abramoff blush.”

That’s not all. The president’s lawyers could also call witnesses to testify about Hunter Biden’s questionable business dealings in other parts of the world, including China and Romania — testimony that would be relevant because it would establish a pattern of corruption.

Finally, they could call the former vice president himself to testify. Questioned under oath, Biden would not be able to get away with the dismissive replies he regularly gives — that “no one has said my son did anything wrong,” and that we should “focus on Donald Trump.” He would be forced to answer questions he has thus far avoided: Why do you think Burisma hired your son and paid him massive sums despite his complete lack of experience in Ukraine or natural gas? What did Obama officials say to you when they raised concerns about Hunter’s business dealings in Ukraine?

Biden has been shaky under mild questioning during the debates. How would he fare under the withering pressure of legal cross-examination? If he stumbled, or appeared confused, it could expose to voters how old and frail he really is at the very moment they are going to the polls to decide their party’s presidential nominee. Do Democrats really want to put Biden through that, especially since they know that the president is going to be acquitted?

And for what? Democrats have no idea what John Bolton will say under oath. His testimony may be exculpatory for the president, in which case they will have opened the Pandora’s box of witness testimony for nothing. So, call your witnesses, Sen. Schumer. They may very well pose a greater danger to Biden’s presidential prospects than they do to Donald Trump.

Follow Marc A. Thiessen on Twitter, @marcthiessen.