Barack Obama said on Friday he has "nowhere to go but up", as healthcare travails drive his presidency to a nadir of popularity.

The president said he would bounce back and that Americans would eventually appreciate his Affordable Care Act, despite its troubled rollout. The reforms will face another crucial test on Saturday, the White House's self-imposed deadline for improvements to be made to healthcare.gov, the federal healthcare exchange.

"The good thing about when you're down is that usually you got nowhere to go but up," Obama told Barbara Walters in an ABC interview set to air on Friday night, according to advance transcripts. He said his poll ratings – currently at their lowest in his presidency – went up and down but that the signature law known as Obamacare would prevail.

"I continue to believe and [I'm] absolutely convinced that, at the end of the day, people are going to look back at the work we've done to make sure that in this country, you don't go bankrupt when you get sick, that families have that security. That is going be a legacy I am extraordinarily proud of."

Smiling and looking relaxed alongside his wife, Michelle, in the White House, the president sought to use his Thanksgiving interview to assure supporters that he was merely experiencing turbulence common to second-term presidents, rather than terminal freefall. He also told Walters he would not run for elected office again.

In a separate headline-grabbing initiative, the Obamas visited immigration reform activists who are staging a hunger strike at Washington's national mall. The "Fast for Families" protesters are refusing food and drinking only water, in an attempt to pressure Congress to reform immigration laws.

Obama praised them for focusing attention on the cause and expressed optimism about reform. During a visit to San Francisco last week, he lauded their sacrifice. "I want them to know we hear you," he said. "We're with you. The whole country hears you."

In the ABC interview, which was taped last week, Obama alluded to reports that administration officials did not relay to him warning signs about the healthcare.gov website in the run-up to its 1 October launch.

"Obviously my most recent concern has been that my website's not working," he said "and we're evaluating why it is exactly that I didn't know soon enough that [it] wasn't going to work the way it needed to. But my priority now has been to just make sure that it works."

The White House has said a "tech surge", upgrading software and hardware, should fix most of the bugs by Saturday, allowing 50,000 users to navigate the site at any one time. Healthcare.gov is used in 36 states to choose insurance under the Affordable Care Act. Engineers have been working through the holiday period to try to meet the deadline.

Obama brushed off alarm that his job approval ratings were the lowest of his presidency. An ABC/Washington Post poll last week also gave him a similarly low percentage – just 41% - for understanding the the problems of average Americans and being honest and trustworthy.

"I got re-elected in part because people did think I was trustworthy and they knew I was working on their behalf," he said. "Very rarely [do] the good things that happen get the same attention as the things that aren't working so well."

Before the launch, Obama promised the website would be as easy to use as Amazon or Kayak, and that people could keep existing insurance plans if they wished. Both pledges have unravelled.