It’s the first generational jab of the Democratic race delivered straight to the gut of the front-runner.

Sen. Kamala Harris was the one to draw first blood, in a sharp response to speculation that she’d be a good running mate for Joe Biden.

“I think Joe Biden would be a great running mate,” the 53-year-old Harris said while campaigning in New Hampshire. “As vice president he’s shown he can do the job.”

Translation: Biden is a 76-year-old has-been who has twice run failed campaigns for president.

It’s part of a narrative that progressive critics of Biden and President Trump are hoping to cement in the minds of voters and the media — that the former vice president is too old, too gaffe-prone, too moderate, and out of step with the new Democratic party.

But the problem is it’s not working.

Since entering the race, Biden has widened his lead among primary voters and is crushing his opponents in key states like Iowa, New Hampshire and South Carolina.

Who’s out of step again?

Biden is showing that he’s just what many voters want — a seasoned voice of reason who is the party’s best hope of defeating Trump.

Alexandria Ocasio-Cortez and her Green New Deal may be the face of the New Democratic Party but it’s Biden who right now is trouncing progressive darlings like Bernie Sanders and Elizabeth Warren.

Biden is sure to have bad days ahead but he’s going to be tough to beat. Polls show that even supporters of Sanders and Warren and the other Democrats in the field pick Biden as their second choice. And right now Biden is beating Trump by double digits in Pennsylvania, which looms as the key test in 2020.

The early primaries play right into Biden’s hands.

The former veep has strong support in Iowa, New Hampshire and South Carolina, and a sweep in those states would mean an early exit for Sanders and Warren.

Harris and the others are counting on Biden to flop, and the California senator’s punch yesterday is only the first of what is sure to be a steady drumbeat of criticism of Biden’s less-than-progressive past on issues like immigration, crime and school busing.

Biden’s opponents are also hoping that Biden shows his age, especially in the upcoming debates, which begin next month.