President Barack Obama’s “if you like it, you can keep it” promise has House Democrats facing a dilemma as they look ahead to a vote on Republican legislation to preserve existing health plans.

“There will be defections,” a House Democratic leadership aide predicted.

The bill, sponsored by House Energy and Commerce Chairman Fred Upton, R-Mich., would give insurance companies the option of continuing all existing health plans for a year. It’s considerably weaker than a proposal by Sen. Mary L. Landrieu, D-La., that would require insurance companies to continue offering existing plans, but the political power of the legislation may be no less potent: Are you in favor of keeping the president’s promise or not?

The problem for the White House, and House Democrats, is this: Keeping those old plans undermines the new insurance exchanges and reforms at the heart of the Affordable Care Act. They’d much rather have people enter the new exchanges and see them take advantage of the options for comprehensive benefits with the law’s other attributes — such as no more penalties for pre-existing conditions and no more gender discrimination — intact. That has presented two additional problems: The website woes have made signing up difficult for many, and others, particularly those making too much money to qualify for subsidies, are seeing higher premiums than they had under their old plans.

In a House Democratic Caucus conference call at the end of last week, leaders, unsurprisingly, said that they would urge a “no” vote on Upton’s bill.

Though the vast majority of Democrats will likely side with leadership, a sizable contingent of vulnerable caucus members — mostly freshmen — are expected to side with Republicans in bids to win over their more moderate-minded constituents ahead of the 2014 elections.

It’s a challenge to Democratic leaders who pride themselves on maintaining party unity — in stark contrast to GOP leaders who regularly struggle to corral their rank and file — and who hail passage of the health care law as their premier legislative accomplishment.

Both factors were weighing on Minority Leader Nancy Pelosi, D-Calif., when legislation came to the floor this summer to delay implementation of the individual mandate by one year. Pelosi lobbied members hard to oppose the bill, even as targeted lawmakers argued that their re-election chances hinged in part on that vote.

In the end, 22 Democrats voted “yes,” a number one senior House Democratic aide said would probably have been higher without Pelosi’s work.

That same aide told CQ Roll Call that a similar scenario could play out this week, and it could be even more of a challenge for Pelosi. Millions have received cancellation notices from insurance companies, despite the president’s promise that they could keep their health plans if they like them, “period” — leading to a rare presidential apology and turbocharging political pressure for a fix in both parties.

“The president has apologized, but that apology will be hollow unless Washington Democrats work with us to actually stop this train-wreck,” said Michael Steel, a spokesman for Speaker John A. Boehner, R-Ohio. “If they do not, the American people will certainly take notice.”

In conversations with CQ Roll Call, many House Democratic aides said that it was crucial to allow “front-liners” to do whatever it takes to keep their seats in the next Congress and not be bullied into upholding the party’s ideological purity.

One staffer for a senior House Democrat suggested the party should rethink broader Obamacare strategy and back some changes to the law.

Democrats, he wrote in an email, have “bitten the reins and been the work horse for this administration time and time again. We’ve defended health reform to the hilt with the promise that once it went into effect, the pain would have been well worth the struggle.

“It may be time to rally around some adjustments to the law,” he continued. “If the president can’t or won’t aggressively confront the insurance industry for exploiting this loophole, we’ve got to be proactive going into ’14.”

But a House Democratic leadership aide countered that the need for party loyalty, and a unified commitment to defending the health law, couldn’t be overstated. While some House Democrats might feel it “safe” to vote for the Upton bill because they don’t see it going anywhere in the Senate, a few Senate Democrats like Landrieu are starting to rally behind similar legislation.

“Members are going to have to realize that, to some extent, you can cause problems in the Senate if there is considerable House Democratic support on some of these things,” said the aide of the adverse effect those Upton “yes” votes could have if they provide leverage to Senate Democrats.

Of course, with the bill not scheduled to come to the House floor until the end of the week, a lot could change. The current legislative text could fall prey to conservative amendments, vaporizing Democratic support. The White House, which is exploring an “administrative fix” to address the dilemma, could unveil a plan that satisfies Democrats and, in their estimation, renders Upton’s bill irrelevant.

In the meantime, front-line Democrats are staying mum on their stances: None of the offices of the 22 Democrats who voted for the individual mandate delay would tell CQ Roll Call how the lawmakers planned to vote come Friday.

Correction 10: 46 p.m.

An earlier version of this post misstated the way 22 Democrats voted on legislation this summer to delay implementation of the individual mandate by one year. They voted “yes.”