Sen. Tim Scott, R-S.C., is delivering the GOP response to Biden's address to the nation.

Biden finished his speech with a great message of hope for Americans who overcame a year of tumult, saying that he is "more confident or optimistic about America."

"Folks, as I told every world leader I ever met with over the years, it's never ever, ever been a good bet to bet against America and it still isn't," Biden said, to a great round of applause. "There is not a single thing, nothing, nothing beyond our capacity. We can do whatever we set our minds to if we do it together. So let's begin to get together."

Biden said that the insurrection at the Capitol on Jan. 6 was an "existential crisis" and a "test" to democracy, and he said that America's enemies were betting that Americans could not overcome divisions.

"They believe we’re too full of anger and division and rage," Biden said. "They look at the images of the mob that assaulted the Capitol as proof that the sun is setting on American democracy. But they're wrong. You know it. I know it."

Biden is correct that his administration has made great strides in the vaccine rollout, but the credit isn’t entirely his. While his numbers are accurate, they miss critical context.

“When I was sworn in on Jan. 20, less than 1% of the seniors in America were fully vaccinated against COVID-19,” he said. “One hundred days later, 70% of seniors in America over 65 are protected.”

When Biden took office on Jan. 20, only two vaccines -- Pfizer and Moderna -- had been authorized for a little more than a month. Supply was low early on, but always expected to ramp up through spring.

The Trump administration had initiated government contracts with the vaccine makers, and tapped the military to help oversee distribution. Trump aides also set up the program for some 40,000 pharmacies to deliver the vaccinations -- a program Biden referenced in his speech.

Biden has since relied on those Trump-era contracts and pharmacy program to expand vaccinations to Americans.

Where Biden can take credit: Expanding government contracts with vaccine makers to buy more doses. He also set up federally run mass vaccination sites, as well as mobile clinics, with a focus on hard-hit areas. And he’s partnered with community centers to help deliver the vaccine in disadvantaged communities.

-ABC News' Anne Flaherty

Lawmakers are expecting different things as they tune in to Biden's joint address Wednesday night.

Sen. Elizabeth Warren, D-Mass., told ABC News on Wednesday that she is "delighted" that big progressive pushes like child care made it into the White House's proposal, calling it a "win." But aides to moderate Sen. Joe Manchin, D-W.Va., told ABC News Wednesday night that the price tag makes him "uncomfortable."

Republicans, however, want to hear the president commit to working across the aisle on the next piece of legislation. As Sen. Tim Scott, R-S.C., puts the final touches on his speech responding to Biden's address, he said he's hoping to address where Democrats and Republicans can find common ground.

"My goal is to just to be myself and share with the country what I think the priorities are and how we can do those priorities together, as opposed to not," Scott told ABC News.

-ABC News Congressional Correspondent Rachel Scott