Kristen Welker says: Biden's ad-lib about getting on Air Force One didn’t pay off — a reminder that ad-libbing can be very dicey.

Hallie Jackson responds: To Kristen's point, his story about DuPont and a well-educated workforce, not in prepared remarks, showed that sometimes that risk can pay off — with murmurs of assent from Democrats in the room.

Trump mocked centrist Sens. Mitt Romney and Joe Manchin for sitting together at the address tonight.

“Interesting that Romney and Manchin are sitting together, and nobody wants to talk to them. I think they’d make a great No Labels Team!” he said in a Truth Social post.

Both members are leaving the Senate at the end of their current terms. Manchin declined to run for president on the No Labels ticket.

Several times in the speech, Johnson has nodded in agreement with Biden.

The president said that an experience for "both sides" is meeting with business leaders and being told what they need most is an educated workforce.

Harris and Johnson nodded in unison.

The last 30-45 seconds on education were a total ad-lib, not in the prepared remarks.

Now Biden is back on script.

Talking about the high cost of prescription drugs in the U.S., Biden joked that anyone who wants to fly on Air Force One with him could go to other countries and get them for much less.

He talked about flying to Toronto, Berlin or Moscow — but then realized he had misspoken and said, “I mean, excuse me — well, even Moscow, probably.”

The comments were not part of his prepared remarks that were sent out by the White House.

Biden is now discussing an early childhood agenda. That used to be part of his Build Back Better plan, which ultimately was trimmed significantly to become the Inflation Reduction Act. Biden advisers, asked about a potential second-term agenda, have pointed to proposals like universal pre-K as top of the list.

There has been very little heckling so far, but aides have encouraged Biden to remember if it happens the audience that matters is watching at home, not in the room: “Barrel through it,” an adviser told NBC News.

Biden has been adding in many off-the-cuff remarks that weren't in his prepared speech.

Presidents typically stick very closely to their speeches on the teleprompter to avoid any missteps.