"They will be satisfied when we have Canadian healthcare and we've eliminated the Pentagon," the White House spokesman told The Hill, in criticizing what he called "the professional left."
Some liberals have been unhappy with President Barack Obama for not pushing their agenda harder and have gone so far as to compare him to former Republican President George W. Bush, Gibbs said.
"These people ought to be drug tested," he said. "They wouldn't be satisfied if Dennis Kucinich was president."
The Los Angeles Times reported Gibbs later issued a statement conceding he had articulated his thoughts "inartfully."
"I watch too much cable, I admit," he said.
Kucinich told the Times Gibbs's comments were inappropriate for someone in his role.
"It's important for him to understand that there is great concern among liberals and a lot of other people about the fact that we have not created enough jobs, that wars are continuing, that civil liberties have eroded and that this is not what we signed up for," Kucinich said.
Deputy Press Secretary Bill Burton said Gibbs "just answered honestly" to questions about frustrations within the administration.
Asked if the frustration within the administration over not getting credit for the successes it has enjoyed extended to the president, Burton answered there are times when "yes, every single person in this building, including the one who lives here, at times can be frustrated with the way some of the things are covered here."
"I would say that any level of frustration that anybody here in this White House has is extraordinarily minimal compared to the focus that people have on the work that they're doing," he added.
Burton said he doesn't think there is "any danger" Gibbs will step down because of the flap.