Liberals need to "buck up" in preparation for November's elections, Vice President Joe Biden said Monday night.

The vice president didn't back off the notion that disillusioned supporters should "stop whining," a sentiment he uttered on Monday in New Hampshire that drew heavy criticism from liberals in the party.

"And so those who — didn't get everything they wanted, it's time to just buck up here, understand that we can make things better, continue to move forward," Biden said during an appearance on MSNBC, "but not yield the playing field to those folks who are against everything that we stand for in terms of the initiatives we put forward."

Biden was asked by MSNBC host Lawrence O'Donnell, in the debut of the host's new program, "The Last Word," whether he'd like to retract his admonition to liberals to stop complaining.

"There are some on the Democratic base, not the core of it, that are angry because we didn't get every single thing they want," the vice president said.

"They should stop that," Biden explained. "These guys, if they win, the other team, they're going to repeal healthcare [reform] and I want them to tell me why what we did wasn't an incredibly significant move that's progressive and helping people."

Biden's initial comments drew criticism from self-described members of the "professional left," whom White House press secretary Robert Gibbs had criticized in similar terms to the vice president's.  

"You're welcome, Joe Biden, for helping to get the more electable Democrat who actually excites voters to be the Democratic nominee — instead of a lame corporate stooge," said Adam Green, of the Progressive Change Campaign Committee, of Biden's remarks.

"How's Blanche Lincoln working out?" he added, referring to the Arkansas Democratic senator the administration had backed against a liberal challenger during a bitter primary campaign.

The administration has been working to shore up the constituencies that propelled President Obama to a historic victory in the presidential election of 2008. But polls show that first-time voters, young voters and labor groups have grown at times ambivalent about the administration's performance in office. The enthusiasm gap between Democrats and Republicans is one of the most important factors in prognosticators' growing sense that the GOP could win back the House this fall.

Obama will be in Madison on Tuesday to rally some of those young voters at the University of Wisconsin, and Biden will be at Penn State to do the same.