Presidential candidate Pete Buttigieg Pete ButtigiegBillionaire who donated to Trump in 2016 donates to Biden The Hill's Morning Report - Sponsored by Facebook - GOP closes ranks to fill SCOTUS vacancy by November Buttigieg stands in as Pence for Harris's debate practice MORE on Thursday called Sen. Elizabeth Warren Elizabeth WarrenOvernight Defense: Appeals court revives House lawsuit against military funding for border wall | Dems push for limits on transferring military gear to police | Lawmakers ask for IG probe into Pentagon's use of COVID-19 funds On The Money: Half of states deplete funds for Trump's 0 unemployment expansion | EU appealing ruling in Apple tax case | House Democrats include more aid for airlines in coronavirus package Warren, Khanna request IG investigation into Pentagon's use of coronavirus funds MORE (D-Mass.) "evasive" for not saying whether her health care plan would raise middle class taxes.

Warren, a candidate for the Democratic party's presidential nomination, didn't directly answer a question asked by Stephen Colbert Stephen Tyrone ColbertColbert implores Pelosi to update 'weaponry' in SCOTUS fight: 'Trump has a literal heat ray' The Hill's Morning Report - Sponsored by Facebook - Washington on edge amid SCOTUS vacancy Juan Williams: Democrats need to bury their divisions MORE during an appearance on The Late Show Tuesday.

"Senator Warren is known for being straightforward and was extremely evasive when asked that question, and we've seen that repeatedly," Buttigieg said Thursday during an interview on CNN.

The mayor of South Bend, Ind., is polling close to 6 percent, according to the Real Clear Politics polling aggregate.

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"I think that if you are proud of your plan and it's the right plan, you should defend it in straightforward terms," Buttigieg said. "And I think it's puzzling that when everybody knows the answer to that question of whether her plan and Senator Sanders's plan will raise middle class taxes is 'yes.' Why you wouldn't just say so, and then explain why you think that's the better way forward?"

Warren is polling in second place behind former Vice President Joe Biden Joe BidenFormer Pence aide: White House staffers discussed Trump refusing to leave office Progressive group buys domain name of Trump's No. 1 Supreme Court pick Bloomberg rolls out M ad buy to boost Biden in Florida MORE.

Health care has become a top issue in the 2020 Democratic primary, with candidates fighting at length over "Medicare for All" in the debates.

Warren supports Medicare for All plan authored by fellow 2020 contender Sen. Bernie Sanders Bernie SandersSirota reacts to report of harassment, doxing by Harris supporters Republicans not immune to the malady that hobbled Democrats The Hill's Morning Report - Sponsored by Facebook - Republicans lawmakers rebuke Trump on election MORE (I-Vt.)

The proposal would replace private health insurance with a single plan run by the government.

But during the Democratic primary debates, Warren has avoided answering whether it would raise taxes on the middle class.

"So, here's how we're going to do this. Costs are going to go up for the wealthiest Americans, for big corporations," Warren told Colbert on Tuesday. "And hard-working middle-class families are going to see their costs going down."

Sanders's bill doesn't lay out how the plan would be paid for.

But Warren argues that overall costs would decrease for those in the middle class because Medicare for All would eliminate the premiums, deductibles and co-pays many people currently pay for their insurance plans.

But Buttigieg and others running for president, including Biden, have said Medicare for All eliminates choice for Americans who want to keep their private insurance.

Buttigieg released his own health care plan Thursday, which would automatically enroll those without insurance. People who have insurance through their employer could keep their plans or join the new government plan.