White House teases Biden will have a 'big boy press conference' as top aides defend his 'lucidity' and respond to claims world leaders are concerned

President Biden is setting up the next hurdle as he proves he is up for campaigning amid calls by lawmakers for him to step back – submitting to what the White House is now calling a 'big boy' press conference.

The commitment came on a day Biden phone into MSNBC and wrote restive congressional lawmakers seeking to provide assurances that he can beat Donald Trump after his shaky debate performance.

'I guess a big boy press conference, we're calling it, and take some questions from you all,' White House national security spokesman John Kirby called it while discussing Biden's schedule.

White House Press Secretary Karine Jean-Pierre also used the term – which came from a reporter who last week wanted to know the nature of the event. Biden will 'hold a press conference - a big boy press conference,' Jean-Pierre said at the White House while battling questions about Biden's health and cognition.

The White House frequently uses the term 'press conference' even for events where Biden stands side-by-side with a world leader and takes two questions from each side, usually calling from a pre-determined list.

The White House says President Biden will hold a 'big boy press conference' on Thursday ¿ suggesting he will submit to multiple questions

The White House says President Biden will hold a 'big boy press conference' on Thursday – suggesting he will submit to multiple questions

The use of the term suggests Biden will speak for longer, or perhaps even venture off his list to call on people who raise their hands, a throwback to rituals of the past.

Applying the term 'big boy' to the upcoming event would also suggest prior press events were something less than that. 

It comes as Biden himself has been asserting his vitality and effort. 

'That's why I've been out. I've been testing myself - been tested everywhere I go. Going out and making the case. The night of that debate, I went out, I was out until two o'clock in the morning that very night. That very night. It drives me nuts, people talking about this,' he said. 

National Security Council Coordinator for Strategic Communications, John Kirby, also used the 'big boy' terminology, which traces to a reporter's question last week

National Security Council Coordinator for Strategic Communications, John Kirby, also used the 'big boy' terminology, which traces to a reporter's question last week

Biden is under pressure to demonstrate his fitness after his disastrous debate against Donald Trump

Biden is under pressure to demonstrate his fitness after his disastrous debate against Donald Trump

Kirby himself was asked to say if he had ever in his experience seen Biden as he appeared on the debate stage with Trump in Atlanta – a performance that Biden has called a 'bad day' and 'terrible.'

'In my experience, the last 2 1/2 years, I have not seen any reason whatsoever to question or doubt his lucidity, his grasp of context, his probing nature, and the degree to which he is completely in charge of facts and figures,' said Kirby.

He said this morning Biden asked him to produce some facts that he had to go back and retrieve. 

Any presidential press conference carries some risk that the president will go off script.

The stakes will be high Thursday, after some Democrats groused that Biden did not sufficiently put doubts aside in his interview with ABC's George Stephanopoulos that aired Friday and Sunday.

He has held multiple campaign events since the debate, but has continued to make gaffes or odd statements.

Asked how he would feel next fall if Trump won the election, Biden responded: 'I’ll feel as long as I gave it my all and I did the goodest job as I know I can do, that’s what this is about,' Biden responded.

(ABC later changed its transcript of the sit-down to read, 'I did the good as job as I know I can do.' 

With a growing number of elected lawmakers calling for Biden to go, Rep. Debbie Wasserman Schultz told DailyMail.com any candidate can have a bad day - or five of them. it.

‘Do you know any candidate in the United States of America that doesn’t have five bad days on the campaign trail? Because I’ve had five and I’m 57 years old,’ she said.

‘This is the problem, is that the press is intricately parsing and separating and dissecting every single word, every single movement. There’s no human being on earth that could withstand that kind of scrutiny.’ 

Biden's presser comes during a NATO summit he is hosting in Washington this week. That will allow him to focus in part on issues like Gaza and Ukraine that, though arduous, might offer welcome relief from questions about his own fitness, age, and acuity. 

At his last press conference, in Bari, Italy, Biden complained when a reporter asked him a question about Gaza when he was standing alongside Ukrainian President Volodymyr Zelensky.