'Challenge me at the convention.' Biden comes out swinging Monday following calls for him to drop out.

Facing continued opposition within his party, President Biden aggressively pushed back against his critics in a new public letter and television interview Monday morning.

Biden's comments came as Congress is expected to return to Washington on Tuesday for the first time since the June 27 debate. Biden’s debate performance, which saw him speaking haltingly and sometimes losing his train of thought, caused significant concerns among fellow Democrats worried about his ability to defeat former President Donald Trump in November.

Five House Democrats have publicly called on Biden to step aside for another nominee to take his place — an unprecedented move just weeks before the Democratic National Convention.

Here's a look at Biden's latest statements and the context behind them.

What did Biden do?

Biden sent a letter to congressional Democrats on Monday saying that he is “firmly committed to staying in this race.” The letter comes a day after Hakeem Jeffries, a New York Democrat and minority leader of the U.S. House of Representatives, organized a meeting of leaders to discuss support for Biden’s candidacy.

The president doubled down on his stance with an unscheduled call into MSNBC’s Morning Joe, during which he told co-hosts Joe Scarborough and Mika Brzezinski, “I am not going anywhere.”

What did Biden say?

The two-page letter rejects the criticism of Biden’s campaign coming from Capitol Hill members and the media. He denied allegations that he is unprepared to be reelected and reiterated the need for unity within the Democratic Party.

“Any weakening of resolve or lack of clarity about the task ahead only helps Trump and hurts us,” he wrote. “The voters of the Democratic Party have voted. They have chosen me to be the nominee of the party.”

“Do we now just say this process didn’t matter?” he asked. “I decline to do that.”

In response to the growing pressure from Democratic lawmakers and operatives calling for Biden to drop out of the race, the president told the MSNBC hosts: “I don’t care what those big names think.”

“Who else do you think could step in here and do this?” Biden asked on MSNBC. “Run against me. Announce for president. Challenge me at the convention.

“I’m not going to explain anymore about what I should or shouldn’t do,” he added. “I am running.”

Watch the full Morning Joe call with Biden:

On Sunday, Jeffries organized a private conference call with several senior House Democrats — including Reps. Jerry Nadler, Adam Smith, Mark Takano and Joe Morelle, all of whom reportedly said that Biden should step down as the Democratic nominee.

Read more about the Jeffries call from CNN: Several top House Democrats say Biden should step aside during leadership call

How did all of this start?

Biden’s poor debate performance on June 27 has caused growing concern over his fitness for reelection. Almost immediately after the debate, the president started facing public calls about whether he should step down as the Democratic nominee.

Those calls have only grown louder in recent days from elected officials, party stalwarts and donors. The Biden campaign has responded by buying more campaign ads, booking more campaign stops and scheduling a high-stakes interview with ABC News last Friday.

What happens now?

The president remains steadfast in his commitment to run for reelection and win. But he faces an increasingly vocal group within his own party questioning his efforts.

Over the weekend, Rep. Angie Craig became the fifth Democratic member of Congress to call on Biden to step aside. Reps. Mike Quigley of Illinois and Lloyd Doggett of Texas repeated their calls for Biden to exit the race.

On Tuesday, Jeffries has planned to hold a caucus meeting with Democratic lawmakers. Jeffries has remained mum on his stance about Biden’s reelection.

With the Democratic National Convention looming a little more than a month away on Aug. 19, the clock is ticking for Democrats to resolve this issue.