WASHINGTON — Kamala Harris had the best campaign roll-out. Amy Klobuchar’s snowy debut showed grit. Sen. Elizabeth Warren’s opening campaign video was a bit odd. Take it from an unlikely armchair pundit sizing up the 2020 Democratic field: President Donald Trump.

In tweets, public remarks and private conversations, Trump is making clear he is closely following the campaign to challenge him on the ballot. Facing no serious primary opponent of his own — at least so far — Trump is establishing himself as an in-their-face observer of the Democratic Party’s nominating process — and no one will be surprised to find that he’s not being coy about weighing in.

Presidents traditionally ignore their potential opponents as long as possible to maintain their status as an incumbent floating above the contenders who are auditioning for a job they already inhabit.

Not Trump. He’s eager to shape the debate, sow discord and help position himself for the general election. It’s just one more norm to shatter, and a risky bet that his acerbic politics will work to his advantage once again.

This is the president whose 140-character blasts and penchant for insults made mincemeat of his 2016 Republican rivals. And Brad Parscale, Trump’s campaign manager, said the president aims to use Twitter again this time to “define his potential opponent and impact the Democrat primary debate.”

But often Trump’s commentary reflects a peculiar sense of disengagement from the events of the day, as though he were a panelist on the cable news shows he records and watches, rather than their prime subject of discussion. He puts the armchair in armchair punditry.

“Personally, I think he missed his time,” Trump said Tuesday, hours after Vermont Sen. Bernie Sanders’ launched his second bid for the White House.

In an interview with The New York Times last month, Trump assessed Harris’ campaign like a talk show regular, declaring her opening moves as having a “better crowd, better enthusiasm” than the other Democrats.

Crowd size was also at play last week when he held a rally in El Paso, Texas, that was countered a few blocks away by one led by former Rep. Beto O’Rourke, a potential 2020 candidate.

“So we have let’s say 35,000 people tonight, and he has 200 people, 300 people,” Trump observed, wildly exaggerating both numbers. “Not too good. In fact, what I would do is, I would say, that may be the end of his presidential bid.”

No candidate has drawn more commentary and criticism from Trump than Warren, the liberal Massachusetts Democrat. Warren’s past claims of Native American heritage prompted Trump to brand her “Pocahontas” and he has shown no qualms about deploying barbs at her.