Biden said he's "feeling good" and pumped his fists in the air as he left the White House moments ago.

He's now on his way to the Capitol to face Congress and the nation.

There was a sea of white as Democrats started to fill the chamber, ABC News' Capitol Hill team reports. The House Democratic Women's Caucus is wearing all white -- along with "Fighting for Reproductive Freedom" pins.

Other members are wearing blue to show support for the Israeli hostages taken after Hamas' October terror attack.

Some Republicans are wearing pins that say "Say her name: Laken Riley" in honor of the 22-year-old nursing student who was killed while out running on the University of Georgia's campus last month. The suspect charged in her death is a Venezuelan migrant who is illegally in the U.S., officials have said.

Some Republican lawmakers are also wearing buttons that read: "Stop the Biden border crisis."

As ABC News is reporting, Biden's foreign policy has come under fire from left, but the right also has something to be unhappy about. Whether to continue to aid Ukraine in its fight against Russia’s two-year-old invasion has opened up as a major difference between the two parties. House Speaker Mike Johnson has stopped a Senate aid package from passing in his chamber, and continuing to fund the war is becoming more unpopular with Republican voters.

On the left, Democrats have disapproved of Biden’s response to the Israel-Hamas war. To put pressure on the administration, protesters launched a campaign to vote "uncommitted" in various Democratic primaries around the country, and Vice President Kamala Harris has recently joined calls for a cease-fire as the humanitarian crisis in Gaza becomes increasingly dire. Biden may want to work to address concerns within his own party.

-Monica Potts, 538

Protesters are staging a sit-in on Pennsylvania Avenue near the Capitol ahead of Biden's speech -- demonstrating in support of the Palestinian civilians in Gaza suffering amid the Israel-Hamas war.

Biden has faced heavy criticism from the progressive wing of the Democratic Party and many in the Arab American community over his response to the conflict, in which he has sought to balance his sympathy for civilians with support for Israel's campaign after Hamas' October terror attack.

Nonetheless, many critics have called on him to more forcefully push for an immediate stop to all fighting as conditions remain dire for civilians in the Gaza Strip. Cease-fire advocates have interrupted other Biden events in the past few months, including an abortion rights campaign rally in January.

Biden in his speech on Thursday night is expected to announce an "emergency" military mission to construct a pier in the Mediterranean Sea on Gaza's coast to get humanitarian aid into the area, according to senior officials.

Meanwhile, family members of Americans who thought to still be held by Hamas will be in the audience as guests of Republican lawmakers.

Biden called on Congress to send him a bipartisan national security bill amid Russia's ongoing war in Ukraine.

"If the United States walks away, it will put Ukraine at risk. Europe is at risk, the free world will be at risk," he said.

Biden also had a message for Russian President Vladimir Putin: "We will not walk away," he said to applause.

"We will not bow down! I will not bow down! In a literal sense, history is watching," Biden said.

Many Republicans have been increasingly skeptical of foreign aid to Ukraine versus spending on domestic priorities like the southern border. Biden and the GOP have not been able to agree on new immigration changes, despite a Biden-backed deal in the Senate.