In public, Nancy Pelosi lectured Donald Trump on the Constitution and wagged a finger at him for characterising her 'strength'. In private, she questioned his 'manhood' — and her disdain for him became public, again, anyway.

'It's like a manhood thing for him. As if manhood could ever be associated with him. This wall thing,' Pelosi privately told House Democrats after a combative, on-camera Oval Office meetingwith Trump, vice-president Mike Pence and Senate Democratic leader Chuck Schumer.

The account was described on condition of anonymity by an aide who was in the room but not authorised to discuss Pelosi's remarks publicly.

In the space of a few hours on Tuesday, the California Democrat nominated for her second stint as House speaker rolled out her approach to the Republican President as the two prepare for two years of divided government.

'It goes to show you: You get into a tickle contest with a skunk, you get tinkle all over you,' she said after Tuesday's meeting, according to the aide.

Pelosi is said to frown on truly blue language. But in public and private, she can be unsparing in her clapbacks, and never more so than during the Trump presidency. She questioned Trump's 'manhood' publicly in October at Harvard University's Institute of Politics, for example. And yet, she's long counseled Democrats to not get into the muck, Trump-style, advising Democrats before the State of the Union address in January not to get in the way of his 'slobbering self.'

On Tuesday, outside the White House, Pelosi predicted Democrats would stay 'dignified.'

Pelosi hardly saved her disdain for Trump for the private audience, letting it rip in slightly more respectful tones a few hours earlier when the president invited journalists into the Oval Office for what were billed as talks over the national budget. What ensued was like a political cage match, with everyone except Pence jumping in with ripostes, setups, lectures and insults. The conflict between Trump and Pelosi dominated the scene, which was replete with gender politics.

Trump alluded to the fact that Pelosi's election as speaker is not assured. AP

The spectacle suggested a fierce, two-year struggle in which Democrats control one chamber of Congress for the first time in Trump's presidency. The new Congress is sworn in January 3, and Pelosi is nominated for her second stint as speaker of the House and second in the line of presidential succession. That carries significant stakes for Trump, who faces oversight investigations into his presidential campaign and administration. Additionally, the House will include a record number of women elected in the #MeToo era — most of them Democrats — injecting gender into the discussion like never before.

In her opening comments in the Oval Office, Pelosi said failed budget talks would result in a 'Trump shutdown' of government — a phrase that might have inflamed him. Instead, Trump said he'd take responsibility for any shuttering of government.

Trump alluded to the fact that Pelosi's election as speaker is not assured.

'Nancy's in a situation where it's not easy for her to talk right now, and I understand, and I fully understand that,' Trump said.

Pelosi raised a hand, then wagged her index finger: 'Mr President, please don't characterise the strength that I bring to this meeting as the leader of the House Democrats, who just won a big victory.'

She kept it clean through a post-Oval Office press conference, suggesting to reporters that she didn't want to embarrass Trump over his misstatement of facts in front of the cameras.

Behind the scenes is another story. Out came her gibe about Trump's masculinity.

On Tuesday, she told Democrats privately, 'He said at the end of the meeting, he said, 'We can go two routes with this meeting: with a knife or a candy. I said, 'Exactly.''

She went with the knife.

'I told him about Ronald Reagan,' Pelosi told the Democrats. 'I said you probably don't know who I spoke most about on the campaign trail — what President I spoke most about. He said, 'Donald Trump.' I said, 'I never mentioned your name.''

Later in private, she told the Democrats: 'I was trying to be the mom.'