Mr. Dreier becomes the seventh member to retire from the California delegation this election cycle, following Republicans Jerry Lewis, Elton Gallegly and Wally Herger, and Democrats Lynn Woolsey, Dennis Cardoza and Bob Filner. California members are known for their longevity, the result of intense gerrymandering, and most of these retiring members are relatively senior. Yet the protection of incumbency all changed with a recent law that created an independent commission to redraw the state’s 53 congressional districts, a process that has upended many of the state’s safest areas.

Mr. Dreier’s own 26th congressional district, which was north and east of Los Angeles, was redrawn in a way that gave Democrats a distinct majority. And while some incumbents whose districts have been altered are now moving to run in adjacent areas, the new California map didn’t provide Mr. Dreier with any nearby area that wasn’t strongly Democratic. While Republicans have used their statehouse wins in the 2010 election to help shore up many of their congressional seats, California was always going to prove tough. Democratic Rep. Grace Napolitano is running in the new district, and is expected to easily win.

Mr. Dreier is retiring at the peak of his powers; he’s been the chairman or ranking member of the important rules committee since 1999, and is a close ally of Speaker John Boehner. And there is some evidence that he’s being pushed by colleagues to now mount a challenge against California Sen. Dianne Feinstein. Back in January, Kevin McCarthy, third-ranking House Republican, suggested Mr. Dreier would prove a good contender for a race that the GOP has so far failed to recruit a top name: “He’s a good member. He has probably statewide name ID, more so, having served,” said Mr. McCarthy at the time. “I think he’s very smart, he’s smart on issues. I think he’d be a big contrast.”

Mr. Dreier hasn’t been doing much by way of fundraising — one hint that this retirement announcement was coming — which suggests a Feinstein challenge isn’t his priority. But at a relatively spry 59 years old, and with a deep knowledge of California politics, Mr. Dreier might not be done with politics.