We knew that former vice president Joe Biden was going to take some heat from his opponents in the first Democratic presidential debate. He has been leading in all major polls, and the quickest way for lower-polling candidates to get noticed is to go after him.

But what we didn’t expect is how directly he’d be attacked, and by whom. A relatively little-known congressman, Rep. Eric Swalwell (D-Calif.), accused Biden of staying in politics too long and basically told him to get out of the race.

“I was 6 years old when a presidential candidate came to the California Democratic convention and said it’s time to pass the torch to a new generation of Americans,” Swalwell said. “That candidate was then-senator Joe Biden. Joe Biden was right when he said it was time to pass the torch to a new generation of Americans 32 years ago. He’s still right today.”

He later repeated the line: “Pass the torch to the generation that’s going to feel the effects of climate change,” he said, yelling over another conversation Biden was having.

It was one of the most confrontational moments of the debate, and Swalwell kind of came out of the blue by being the one to give it.

He is not in the top or even second tier of the Democratic presidential candidates. He’s not even polling at 0.1 percent in an average of recent polls. He barely qualified for the first Democratic debate. To the extent he’s in the news, it’s been because he’s made his campaign almost entirely about gun control.

“There’s a lot we can do with this issue, but unless it’s the number one issue for a president, it’s just going to be one that we respond to shooting after shooting,” he told CNN’s Jake Tapper in April when he became the 18th Democratic presidential candidate.

Swalwell has been saying Biden is the candidate of yesterday for a couple weeks now, but it hadn’t broken through as it did Thursday night. Up until the debate, Swalwell’s criticism certainly hadn’t received as much notice as the other 2020 opponents who pressure Biden to change his mind on policy.

Swalwell was not a major voice sharply criticizing Biden for supporting bans on federal funding for abortion, as the female senators in the race were. Nor does Swalwell make Biden’s work on a 1994 tough-on-crime bill part of his own stump speech about guns and criminal justice. And it was Sens. Cory Booker (D-N.J.) and Kamala D. Harris (D-Calif.) who swung punches at Biden when Biden talked about being chummy with segregationist senators in the 1970s.

Biden’s 2020 opponents had been trying to hint for weeks that Biden is out of touch with the Democratic Party of today. On the biggest stage possible, Swalwell just out and said it.

But in hindsight, maybe we should have seen this “pass the torch” attack on Biden coming. For one, Swalwell has said something to that effect before.

“We can’t have a candidate whose ideas are staler than Donald Trump’s,” he said on CNN recently. “I don’t think we can have a candidate who’s been in government for the past 20 years; I don’t think that’s gong to work.”

Another aspect of Swalwell’s campaign is that he’s a millennial. At 38, he’s one of the youngest candidates in the race. (South Bend, Ind., Mayor Pete Buttigieg is one year younger.)

Swalwell has a 2-year-old and a 7-month-old, and he recently filmed an ad showing him changing his daughter’s diaper as a metaphor for how he would clean up Washington.

So even though he’s a four-term congressman, part of Swalwell’s brand as a presidential candidate is that he’s part of a new wave of young Democrats with fresh ideas. Biden, at 76, is one of the oldest candidates in the race. And to Swalwell, he’s literally standing in his way.

With the exception of Sen. Bernie Sanders (I-Vt.), most of Biden’s nearer 2020 opponents have avoided attacking him for a couple reasons. He’s the most senior Democrat in politics today. He represents the Obama presidency — and a potentially powerful voting coalition. It’s too early, strategically, for candidates such as Harris, Sen. Elizabeth Warren (D-Mass.) or Buttigieg to take the gloves off and go negative.

But the calculation changes when you’re at the bottom rung and have nothing to lose. Up until this moment, most people paying attention to the presidential race hadn’t even heard of Swalwell. We have no idea how lasting his attack on Biden will be — Harris’s confrontation with Biden on race seems much more resonant. But it certainly got Swalwell his 15 minutes of political fame.