With admirable poise given the explosions around them, President Trump’s lawyers began their second day of defense with a point-by-point dissection of the case against their client.

They calmly focused on the transcript of Trump’s July 25 call with the president of Ukraine, with Jay Sekulow saying it involved no “violation of an oath.”

Ken Starr, in a learned but too-long presentation on the history of impeachment, called out Speaker Nancy ­Pelosi’s “runaway House” and said the partisan product she ­produced was “dripping with fundamental process ­violations.”

There was more, and it was all solid stuff that, on any other day, might have been a final nail in the Democrats’ teetering case. Unfortunately for the defense, Monday already had been claimed by John Bolton, and he wasn’t even in the room.

Bolton had instead sent a thunder bolt by authoring “The Room Where It Happened,” a clever book title surely lifted from a scene and song in the Broadway hit, “Hamilton.”

How fitting — and inevitable — that history, politics and theater would collide during the impeachment of Donald Trump.

It was also inevitable that Bolton would come back to haunt Trump. Brutally fired after just 17 months as national security adviser, he is now firing back in sensational fashion.

According to passages leaked to the anti-Trump media, Bolton writes that Trump admitted to him there was a link between the president’s demand for investigations by Ukraine and his pause on releasing military aide.

The claim buttresses the first article of impeachment, and Trump quickly called it false. He also accused Bolton of trying to sell a book. Given the provocative timing and title, money is certainly part of the motivation for Bolton and his publisher.

Recall that in recent weeks, Bolton made it clear he was eager to testify, and now he will probably get his wish — just as the book goes on sale. Ka-ching! Ka-ching!

Even before this, at least two Republicans, Mitt Romney of Utah and Susan Collins of Maine, were seen as likely to break with the GOP and join 47 Dems calling for witnesses. Now the dam could break, possibly creating a solid majority for adding testimony and documents to the House record.

An important question will be how many witnesses, and whether Joe Biden and/or his son, Hunter, will be among them. Trump’s lawyers savaged both Monday, a tease to what the Bidens could expect as witnesses.

Still, there is no reason to believe Trump is headed for conviction and removal. Far from it.

For one thing, the requirement for 67 votes — which would mean 20 Republican switchers — remains out of reach. For another, there are many weaknesses in the case against Trump, not the least being that we are now just months from an election.

The longer the trial goes on, the closer the election and the stronger the argument becomes to let voters decide.

Moreover, Bolton’s accusation doesn’t change a key element of Trump’s defense — that he released the aid to Ukraine without getting the investigations he wanted. Even if one assumes it’s true the president outlined a quid pro quo to Bolton in August, he abandoned it in September and got zero benefit.

In that sense, the situation recalls the failed efforts by special counsel Robert Mueller to build an obstruction case against Trump in the Russia probe. There was testimony that Trump ordered aides to fire Mueller, but none did, and Trump didn’t pursue the matter or in any way block the special counsel’s probe.

Over the next few days, as the first stage of the trial comes to a close, the usual predictions of Trump’s imminent demise will fill the airwaves and headlines, courtesy of the usual suspects. Don’t fall for the cheerleading.

Even with Bolton, the basic facts in the Ukraine matter remain too light and too small to bear the enormous burden of removing an elected ­president.