In an ill-timed moment, Rep. Lauren Boebert, R-Colo., shouted at the president, blaming him for the deaths of the 13 U.S. servicemembers killed in an attack at the Kabul airport in Afghanistan last summer, as Biden spoke about veterans exposed to burn pits developing "cancer that would put them in a flag-draped coffin."

"You put them in, 13 of them!" she yelled.

But her words came out just as the president was about to mention the death of his son, Beau Biden, an Iraq War veteran who died from brain cancer in 2015.

"I know," Biden began, attempting to reference Beau. But before he could get the sentence out Boebert shouted.

The members in the chamber immediately booed her.

"One of those soldiers was my son, Major Beau Biden," the president continued. "I don’t know for sure if the burn pit that he lived near, that his hooch was near in Iraq and earlier than that, in Kosovo is the cause of his brain cancer, the diseases of so many other troops. But I am committed to finding out everything we can."

Boebert later addressed the moment on Twitter, saying, “When Biden said flag draped coffins I couldn't stay silent. I told him directly he did it. He put 13 in there. Our heroic servicemen and women deserve so much better.”

-ABC News' Mariam Khan

Biden took a few moments to thank retiring Supreme Court Justice Stephen Breyer for his service on the bench and asked the justice to stand and be recognized.

Breyer has been one of the most loyal attendees of State of the Union addresses over the past 20 years -- and tonight he was clearly touched by the presidential tribute.

Biden then immediately pivoted to his nomination of Judge Ketanji Brown Jackson to fill that seat.

“Since she’s been nominated, she’s received a broad range of support," Biden said.

-ABC News' Devin Dwyer and Justin Gomez

On the pandemic, Biden outlined four "common-sense" steps the U.S. is taking to "move forward safely":

1. Vaccines and treatments: "We will never give up on vaccinating more Americans," Biden said. He also discussed progress on anti-viral treatments and announced a “test to treat” initiative for COVID-positive Americans to obtain Pfizer pills free of charge.

He also announced that starting next week Americans would be able to order even more free rapid tests at .

2. Preparing for new variants: Biden said instead of months or years, we'll be able to deploy new vaccines "within 100 days."

3. Ending shutdowns: Biden stressed the importance of people working in offices safely and keeping schools open. "The vast majority of federal workers will once again work in person. Our schools are open. Let’s keep it that way," he said.

4. Vaccinating the world: Biden said the U.S. has so far sent 475 million vaccine doses worldwide, "and we won't stop."

Sen. Joe Manchin, ., sat with Sen. Mitt Romney, R-Utah, and Republicans during the State of the Union.

“Senator Manchin sat with his colleague Senator Romney to remind the American people and the world that bipartisanship works and is alive and well in the U.S. Senate,” Samantha Runyon, a spokeswoman for Manchin, told ABC News in a statement.

Manchin, who opposed many of President Biden's proposals including the original version of his Build Back Better plan, was seen applauding during several moments when the president outlined his agenda.

-ABC News' Mary Bruce and Trish Turner

The nation's capital has ramped up security ahead of Biden's first State of the Union address tonight.

Up to 700 National Guard troops have been made available to assist local law enforcement, and a controversial inner-perimeter fence once again surrounds the U.S. Capitol.

The U.S. Capitol Police have also been working in tandem with local, state and federal law enforcement agencies on a "security plan to prevent any disruption to the important work of Congress," Capitol Police Chief Tom Manger said in a statement earlier this week.

-ABC News' Noah Minnie