Still, the politics of the issue could change quickly as Democrats face pressure to show they are responding to public frustration with the website. Ten Democratic senators have signed a letter asking the White House to extend the date beyond March 31 — six of those are up for reelection in 2014.

Sen. Jeanne Shaheen (D-N.H.) said an extended enrollment was merely a fair way to make up for a website rollout she labeled a "disaster." Millions of people have been shut out of the site intended to link consumers with private health plans. "That is unacceptable; consumers should not pay a penalty because a website did not work," Shaheen wrote in an op-ed published Wednesday in USA Today.

Advocates for the extension note that the administration has already pushed back the date by six weeks in an attempt to align mismatched deadlines outlined during the rule-making process. Another limited extension is unlikely to change consumer behavior much, some experts opposed to a delay concede.

"To change sends a message: Don't worry about signing up quickly. So there is an impact, but it depends a lot on how long an extension it is," said Linda Blumberg, a health policy expert at the Urban Institute.

Blumberg said it was too soon to know whether an extension was necessary. Any decision should come only after insurers know who is signing up and whether they are seeing too many sick customers to deliver on the premiums they've promised. There are two major provisions already built into the law to help insurers adjust for risk pools, she said.

Obama advisors made similar arguments. Extending the enrollment period by a few months or a year increases the possibility that people won't sign up until they're too sick, increasing the costs for everyone else, said Chris Jennings, a former advisor to President Clinton now working on Obamacare implementation.

Enforcing the requirements for insurers without enforcing those for individuals would compound the destabilizing effect, Jennings said.

"No one will sell you house insurance when your house is on fire," he said. "If you want to ban discrimination against people with preexisting conditions, then you have to have everyone in the pool. That's why you need the individual responsibility requirement."

Critics of the president's law are reviving the push to undo the mandate. Romney issued a statement Wednesday suggesting a number of changes, including "carefully phasing it in to avoid the type of disruptions we are seeing nationally."

In support of the Obama plan, some former Romney advisors have stepped forward to counsel patience through what they suggest is just a rocky beginning.

The law ramped up slowly in Massachusetts, said Jonathan Gruber, an MIT economist who has advised Romney and Obama on healthcare reform.

In the first month of enrollment in 2006, he said, only 123 enrollees from the premium-paying population — comparable to the group using the marketplaces created by the Affordable Care Act — signed up. That represented fewer than 1% of those who eventually signed up within the enrollment period.

"The fact that people aren't signed up now for a policy they can't even get until January, and which they're not mandated to have until March, is not at all interesting or important," Gruber said on a White House conference call held as Obama prepared to travel to Boston. "What matters is the fact that it will ramp up, and it will ramp up over time."

The arc of enrollment in Massachusetts suggests that the deadline itself plays an important role, he said.

As the program neared the deadline, he said, "you saw an enormous increase in healthy people signing up."