A new Iowa poll out Saturday showed Sen. Bernie Sanders, Vermont's independent Senator, coming within seven points of Democratic frontrunner Hillary Clinton. But pollster Ann Selzer, the president of Selzer & Company, said it's not motivated by anti-Clinton sentiment.

"Her support is going a little bit into the not-sure category with people being sort of waiting there. But the Bernie Sanders vote it certainly getting stronger," Selzer said on CBS' "Face the Nation" Sunday. "It isn't just that there's an anti-Clinton sentiment...When we ask Bernie Sander supporters is this because you align with Bernie Sanders, the person and his views, 96 percent say yes. Overwhelmingly, that's what they're up to."

Although Clinton lost a third of her support and received less than 50 percent support for the first time in Iowa, Selzer said her favorable numbers remain strong.

Sanders might still be losing to Clinton overall, but he's up among people who say they will participate in the Iowa caucus for the first time, those who consider themselves independent, and people under 45.

"That's the Obama coalition. Those are the groups that he put together that surprised Hillary Clinton in 2008," she said.

Vice President Biden, who received 14 percent support in the poll, draws about evenly from people who would support Clinton and Sanders, Selzer said. He has good favorable numbers, which creates an opportunity. Plus, she added, when her polling firm asked Clinton supporters if they would be comfortable if Clinton dropped out of the race and Biden hadn't declared a candidacy, 51 percent said they'd like another candidate in the mix.

On the Republican side, businessman Donald Trump is still blowing away the rest of the field with 23 percent support.

"He has grown his favorability and it's turned into votes," Selzer said.

Weighing in on Trump's rise in a separate "Face the Nation" interview, fellow Republican candidate Bobby Jindal said Trump has done well because "he's hit a nerve."

"Voters are telling me they're frustrated, not just with President Obama and the Democrats. They're frustrated with the Republicans as well," Jindal, the Louisiana governor, said.

But Jindal - who is the first choice of just two percent of Iowa Republicans surveyed in the poll - thinks he has a shot.

"As the voters get serious, as we get past these summer months, they're going to start asking the question of who can actually do this job. Who has the intelligence? Who has the courage? Who has the experience? I think when that happens, we're going to do very well," Jindal said. "What I see in the polls is that nobody has any votes right now. I think the voters in Iowa, these early states, want to kick the tires, ask the tough questions. They're not going to decide until much later in this process."

The only other Republican candidate who received double-digit support was neurosurgeon Ben Carson, who was the first choice of 18 percent of those polled. Selzer said he was not unlike Mike Huckabee, the former Arkansas governor who won the 2008 Iowa caucus and is running again in 2016.

"Nobody is really doing much on television, but he has billboards quite everywhere. So Ben Carson is in your community really on a pretty widespread basis," she said. "People know him."

She pointed out that if you total the support for Trump, Carson and former Hewlett-Packard CEO Carly Fiorina, 46 percent of Iowa Republicans are picking someone who comes from outside of government.

"That says something about the mood," she said.

Things don't look good for former Florida Gov. Jeb Bush, who is not making improvements in Iowa, and Wisconsin Gov. Scott Walker, a onetime favorite who has seen his support drop from 17 percent in May to 8 percent in the latest poll

"Jeb Bush's numbers don't look very good here," Selzer said. As for Walker, she conceded that things have been quieter for all other candidates since Trump entered the race.

But, she added, "I think he's just not out there in a big way in a big presence so his support has been cut in half."