WASHINGTON — Mayor Lori Lightfoot attended the Democrats’ closing arguments in President Donald Trump’s Senate impeachment trial on Friday, watching technically as a former federal prosecutor and politically as someone whose top national priority is to replace Trump in the White House.

“My old trial lawyer instincts certainly kicked in as soon as I was in there and watching Justice Roberts,” Lightfoot told me after she emerged from the Senate gallery, referring to Supreme Court Chief Justice John Roberts, presiding over the trial.

Lightfoot said she “paid attention to the former prosecutors” — Democratic senators Amy Klobuchar, Minnesota; Kamala Harris and Dianne Feinstein, California; and Patrick Leahy, Vermont.

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She also closely observed Roberts.

“I have to wonder, when he bears witness to the entirety of this trial and as somebody who cares deeply about the institutions of government, by all accounts, what that will do for him in thinking about a very divided court.

“What will he do both as an individual, but also as the chief judge to think about ways in which the Supreme Court can be the adults in the room, if you will?”

Friday was the last of three days the House impeachment managers had been allotted to argue for Trump’s removal from office — unlikely, since Republicans are sticking together.

On Saturday, Trump’s defense presents opening arguments. In contrast to marathon Democratic presentations, his legal team told reporters Friday to “expect a short day tomorrow.”

The light Saturday schedule could be due to a Friday tweet from the ratings-conscious Trump, who grumbled, “looks like my lawyers will be forced to start on Saturday, which is called Death Valley in T.V.”

The Democrats on Friday argued Trump obstructed Congress; at the same time, they tried to anticipate — and dilute — what they expected from Trump’s defense. The House filed two articles of impeachment against Trump: obstruction of Congress and abuse of power.

Democrats are working two audiences: the GOP senators, in the hope of finding four who will join them to force witnesses and documents; and the public, who may be following the trial only sporadically.

House impeachment manager Rep. Hakeem Jeffries, D-N.Y., distilled the essence of the case against Trump, repeating several times that Trump “tried to cheat. He got caught. And then worked hard to cover it up.”

Lightfoot endorsement update

Earlier Friday, Lightfoot moderated a panel at the U.S. Conference of Mayors meeting — the reason she is in D.C. this week — with nine other mayors who had grappled with mass shootings.

On Capitol Hill, she met with Harris in her Senate office before heading to the trial. Harris, when she was in the presidential race, had sought Lightfoot’s backing.

At one time, there were six senators in the 2020 contest. On Friday, Lightfoot was peering down at the four still running: Klobuchar; Bernie Sanders from Vermont; Elizabeth Warren from Massachusetts; and Michael Bennet from Colorado.

Lightfoot told me Thursday she will endorse a Democratic presidential candidate before the March 17 Illinois primary and she was likely ruling out Sanders, Warren and former Vice President Joe Biden. All three very publicly supported the Chicago Teachers Union strike — and never contacted her to ask for her backing.

David Mellet, Lightfoot’s political chief, told me on Friday:

*After my column posted, Biden’s campaign contacted him on Thursday and Warren’s on Friday; so far, they have not connected.

*Lightfoot will not endorse until after Iowa, New Hampshire, South Carolina and Nevada cast the first presidential votes in February.

*Ex-New York Mayor Mike Bloomberg’s team is aggressively courting Lightfoot; she knows him the best and appreciates his vow to continue to spend his millions to defeat Trump even if he is not the nominee. Mellet told me: “I don’t believe at this point there is a front-runner.”