Schiff Led the ‘Nerd Caucus’ Before the Trump Era. Now He’s a Senate Favorite.

Before Representative Adam B. Schiff became famous as the chief congressional tormentor of former President Donald J. Trump, his professional hallmark was his low profile.

In a Southern California district glittering with show business, he was simply “the congressman from Burbank.” In a state teeming with Democratic political stars, he was rarely on short lists for higher office. In Congress, his calling cards for years were the Democratic Study Group on National Security — also known as “the nerd caucus” — which he co-founded, and his knack for securing federal dollars for light rail in Greater Los Angeles.

Now Mr. Schiff is a national figure and the favorite to become the next California senator, buoyed in his liberal-dominated state by his anti-Trump bona fides: lead manager during the former president’s first impeachment trial and proud recipient of a censure once Republicans took control of the House.

As Tuesday’s primary draws near, Mr. Schiff is the Democratic front-runner, and polls suggest he may be on a glide path to the seat, which was held by Senator Dianne Feinstein for more than 30 years until her death at age 90 in September.

A coveted endorsement last year from the former House Speaker Nancy Pelosi, a longtime ally, unleashed a gusher of support from influential Democrats and wealthy donors, including from tech billionaires in recent days. None of Mr. Schiff’s two dozen or so rivals have come close in fund-raising.

And, to the frustration of the most liberal Democrats, he and his allies have shrewdly maneuvered to sideline the woman who was the biggest threat to his election, Representative Katie Porter, by spending a barrage of campaign funds to elevate a novice Republican candidate, the former baseball star Steve Garvey.