President Barack Obama is making another attempt today to sell his health care law to the public. He learned Wednesday that he’s got more work to do than he expected.

When the House passed two Republican measures to delay core provisions of the law, unexpectedly large numbers of Democrats took the opportunity to endorse the proposals: 17 percent of them voted to delay the coming employer mandate by one year and 11 percent voted to put off for the same time the requirement that individuals obtain health insurance.

Most notable on the list were two congressmen who voted to enact Obamacare three years ago and are favored to hold open Senate seats for their party next fall: Gary Peters, who at the moment looks like a safe bet to succeed Carl Levin in Michigan, was a “yes” on both bills. Bruce Braley of Iowa, who has the clear edge in the race to succeed Tom Harkin, supported the employer mandate postponement.

These were show votes, to be sure, because neither bill will ever come up for a vote in the Senate — the same way the Democratic majority there has ignored the three-dozen previous times the House has voted to repeal or delay all or part of the law.

But the relatively large number of Democrats who spurned the president underscored the anxiety the party feels about thriving in the midterm elections if Obamacare remains as unpopular as it is now.

The most recent poll on the subject, taken last month by NBC and the Wall Street Journal, found just 37 percent labeling the law a good idea, while 49 percent dubbed it a bad idea. This is a main reason why the administration has started to intensify its public relations campaign and moved on its own to delay the employer mandate.

Presumably, following the president’s lead is why 35 Democrats felt free to cross their party leaders and endorse the delay in the employer mandate. But political self-preservation has to be the only reason 22 of those lawmakers also voted to postpone the individual requirement.

Almost all of them either opposed the measure when the House cleared it in 2010 or have been elected to the House since, and the majority of them are already anticipating expensive and intense races for re-election during the next 15 months.

In addition to Peters, the Democrats who voted for both bills were Ron Barber, Kyrsten Sinema  and Ann Kirkpatrick of Arizona; Julia Brownley, Raul Ruiz and Scott Peters of California; Cheri Bustos, Bill Enyart and Brad Schneider of Illinois; Dan Maffei, Sean Patrick Maloney and Bill Owens of New York; Joe Garcia and Patrick Murphy of Florida; John Barrow of Georgia; Jim Matheson of Utah; Mike McIntyre of North Carolina; Collin C. Peterson of Minnesota; Nick J. Rahall II of West Virginia; Elizabeth Esty of Connecticut; and Pete Gallego of Texas.