The Senate's second-ranking Democrat on Tuesday accused GOP presidential candidates of holding a poor grasp on reality when it comes to their positions on raising the debt limit.

Senate Majority Whip Dick Durbin (D-Ill.) singled out Rep. Michele Bachmann (R-Minn.) and former Minnesota Gov. Tim Pawlenty (R), accusing them of promoting irresponsibility and rooting for a default on U.S. debt.

"I listen to these Republican presidential candidates, this former governor of Minnesota who says he's praying for a default. Michele Bachmann just ... hoping that we have a default," Durbin said on MSNBC.

"They don't understand reality," added the Illinois Democrat. "And here's what the reality will be: On Aug. 3, if we default, we'll have $172 billion to pay our bills in August, and the bills total $306 billion."

It's somewhat unusual for a sitting Democratic lawmaker to launch an attack against a GOP presidential candidate at this relatively early stage of the campaign. But Senate Democrats have already shown a willingness to cross that boundary, having attacked Bachmann earlier this month, accusing her of rooting for a bad economy.

Pawlenty has said before that he doesn't favor raising the debt limit, especially if it's not attached to an ironclad agreement to cut spending.

"President Obama is lecturing the country instead of leading it," Pawlenty said Monday night in reaction to the president's speech. "He has presided over the largest and most irresponsible run-up of debt in our nation's history, and he now threatens to preside over the first default in U.S. history."

Bachmann, meanwhile, was defiant and renewed her vow to vote against raising the debt limit.

"The Congress and the president should not raise the debt limit," she said. "Rather than scaring seniors and veterans, it’s time to make the tough choices and make the spending cuts necessary to put our nation on the path to prosperity, lower spending and a balanced budget.”

Watch Durbin below.

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Daniel Strauss contributed.