Rep. Waxman, key ObamaCare architect, to retire after 20 terms in office

June 18, 2012: Rep. Henry Waxman speaks on Capitol Hill in Washington. (AP)

Longtime Democratic Rep. Henry Waxman announced Thursday he will not seek reelection in the fall, becoming the latest architect of the Affordable Care Act to announce his retirement.

"After 40 years in Congress, it's time for someone else to have the chance to make his or her mark," the California congressman said in a statement.

Waxman will have served 20 terms in Congress by the time of his retirement. As prior chairman of the House Energy and Commerce Committee, he was instrumental in the drafting of ObamaCare in 2009.

Two other Democrats involved in that process -- Rep. George Miller, D-Calif., and Sen. Max Baucus, D-Mont. -- have also announced their retirement from Congress (though Baucus is awaiting confirmation to be the next ambassador to China).

Republicans swiftly characterized Waxman's decision as a sign of Democratic vulnerability.

Rep. Greg Walden, R-Ore., chairman of the National Republican Congressional Committee, said "it's a clear indication that House Democrats think they won't be wielding the gavel" after the midterm elections in the fall.

"With the way ObamaCare is playing out they have a tough battle to hold ... onto what they've got," he said.

In a lengthy statement announcing his decision, Waxman said he takes pride in his legislative accomplishments, listing among them the Affordable Care Act. He called its passage the fulfillment of "one of my lifelong dreams."

President Obama, in his State of the Union address, defended the health law against ongoing efforts by Republicans to undermine it. Technical problems with the launch of insurance exchanges last year raised questions about the law's viability, but his administration has tried to address those issues and says enrollment is improving. Still, the rocky launch could cause problems for incumbent Democrats who voted for it.

Waxman leaves Congress after a career spanning four decades. He also co-authored a controversial cap-and-trade bill which would have effectively charged businesses for greenhouse gas emissions. In 2012, he ran into controversy after he accused Republicans of acting "like terrorists" by trying to force the administration to approve the Keystone oil pipeline.

"When I was first elected to the House - in 1974 - I hoped to be able to serve 20 years and leave a mark on some important issues," he said. "I never imagined I would be in the House for 40 years and be able to advance every issue I care deeply about.  But in what feels like a blink of an eye, it has been 40 years and I've devoted most of my life to the House of Representatives."

Fox News' Chad Pergram contributed to this report.