Decorah, Iowa (CNN) Pete Buttigieg on Thursday accused Joe Biden and Bernie Sanders , by name, of forcing the debate among Democratic presidential contenders to be too focused on the past rather than the future.

Buttigieg's naming of his rivals is a significant shift just days ahead of the Iowa caucuses, something the former mayor of South Bend, Indiana, has avoided doing in recent weeks. The move signals that Buttigieg sees the former vice president and the Vermont senator as his main opponents in the key early state.

"I hear Vice President Biden, saying that this is no time to take a risk on someone new," Buttigieg said. "But history has shown us that the biggest risk we could take with a very important election coming up is to look to the same Washington playbook and recycle the same arguments and expect that to work against a president like Donald Trump, who is new in kind." Earlier this month the Biden campaign released an ad in which a narrator tells voters, "This is no time to take a risk."

Buttigieg then went after Sanders.

"Then I hear Senator Sanders calling for a kind of politics that says you got to go all the way here and nothing else counts," he said. "And it's coming at the very moment when we actually have a historic majority, not just aligned around what it is we're against, but agreeing on what it is we're for."

Buttigieg has made both of these points before, but Thursday's town hall in Decorah represents the first time the former mayor has taken on his opponents by name. Buttigieg even strenuously avoided mentioning Sanders by name in a lengthy gaggle with reporters that focused on how the former mayor's campaign was fundraising off Sanders' surge in Iowa.

Buttigieg then continued with the thrust of his argument: The debate between Biden and Sanders, the two Democrats leading in most statewide polls in Iowa, are too focused on the past.

"Look, I feel very strongly about the Iraq War, but hearing arguments over who said what when the 2003 is, leaving aside the fact that this is 2020 and we've got, not only to learn the lessons of the war in Iraq, but to make sure we don't get sucked into a war with Iran," Buttigieg said.

He added: "I feel passionately about protecting Social Security. That's exactly why I don't want us to get caught up in an argument over who said what when about Social Security in the 1990s when Donald Trump is threatening Social Security and announcing cuts to Medicaid today. That's happening today."

Biden and Sanders sparred over their respective records on the Iraq War during a debate earlier this month in Iowa. And the two campaigns have been engaged in a tense back-and-forth over their past comments about Social Security.

Biden responded to Buttigieg on Thursday by making light of the comments, telling reporters that he didn't know "what Pete's talking about."

"He's a good guy, and that must be a sign that things are getting a little tight," Biden said at an Iowa Dairy Queen. "A Washington playbook, I'm not sure what he means. what I'm advocating for the American people, the middle class and giving people a shot, and a Dairy Queen!"

After the town hall, Buttigieg discussed his criticism of Biden and Sanders with reporters.

"I want to make sure that, as we go into these closing days, there is a clear understanding of the different paths that we offer," he said. "I am meeting so many Iowans who are focused, above all, on making sure that we win and defeat this President."

He added: "I think the way to do that is to move past the old arguments that have dominated the conversation, turn the page and on something different. And it is just a different approach to what Vice President Biden or Senator Sanders are offering and I want to make sure that choice is as clear as possible, especially for Iowans still making up their mind in these crucial final hours."

Buttigieg said he was not concerned that calling them out by name would be a turn off for prospective Iowa caucusgoers.

A Monmouth University poll released this week found Biden at 23% in Iowa and Sanders at 21%, with Buttigieg trailing both of them at 16%.

This story has been updated with a response from Joe Biden.