Story highlights McCaskill, a Democrat said Biden is a "sweet, nice guy" but it might be unwise for the vice president to take on Clinton

She also criticized other Republican candidates for failing to take on Trump more directly over his recent comments about women

Washington (CNN) Missouri Sen. Claire McCaskill said Wednesday the surge in popularity for both Republican Donald Trump and Democratic socialist Bernie Sanders can be attributed to popular "cynicism" about Washington.

"People are really aggravated at the government right now," McCaskill, a Hillary Clinton supporter, told CNN's "New Day" on Wednesday. "There are a lot of people that are just going 'Really? You guy's can't get anything done? All you do is fight.'"

McCaskill said that Trump and Sanders also come at the problem of unhinged political donations from different angles, too. Trump is wealthy and doesn't need any donations and Sanders eschews the money almost completely. Combined, they nail popular sentiments about Washington and politicians.

"I think there is a huge amount of cynicism and frustration with the government writ large," McCaskill said.

McCaskill is backing Clinton just as Sanders is rising in the polls in New Hampshire and questions about Clinton's use of a personal email server persist. The former secretary of state promised to turn over the entire server to federal investigators Tuesday night.

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