MARION, Iowa – To Bernie Sanders, President Barack Obama's improbable victory in the 2008 Iowa caucuses was a testament to the power of an inspirational underdog. To Hillary Clinton, Obama's win over her eight years ago proved the importance of a robust and refined political apparatus.

The Democratic presidential candidates' theories are driven in part by necessity — Sanders' has undeniable energy heading into the final week of campaigning in Iowa, while Clinton has a massive field operation that's been on the ground for nearly a year. But they also reflect their competing visions of what Democratic voters are seeking in the 2016 election.

Sanders is running on a pledge of political revolution, one that builds on what he sees as the country's great moments of change: the rise of trade unions, the legalization of gay marriage, and yes, Obama's unexpected victory in the 2008 Iowa caucuses.

"Eight years ago, all over this country people said an African-American becoming president of the United States, you're nuts, that can't happen, too much racism in America," Sanders said during a campaign stop Saturday. "And you think he's going to win in a very white state? Ain't going to happen. You made it happen. You made history."

Clinton believes Democrats are looking less for another big moment of change and more for a steady hand who can build on Obama's progress, but perhaps be more adept at managing Washington's grinding gridlock.

"I believe I have the experience, the judgment and the vision to get us back moving, further than we got with President Obama," Clinton said Sunday during an event in Marion.

Of course, Obama was successful in 2008 because he had both an inspirational message and a top-notch political organization. The Feb. 1 Iowa caucuses will be the first test of whether voters want Sanders or Clinton to follow him.

In a year when voters appear eager to abandon the political elite, Clinton — a former first lady, senator and secretary of state — has embraced her standing as the favored candidate of the Democratic establishment.

Several senators were campaigning in Iowa on her behalf, including New Jersey Sen. Cory Booker, who introduced Clinton at an event in Marion Sunday. The heads of Planned Parenthood and the Human Rights Campaign, one of the largest gay rights organizations, also joined Clinton on the campaign trail Sunday.

While Obama was an underdog in the 2008 race, he did have significant support among state and national officials. Sanders has not been endorsed by any of his fellow senators, nor does he have the backing of any prominent Iowa officials.

Asked whether the backing of Democratic officials matter, Sanders' campaign manager Jeff Weaver said: "People matter."

The people that matter most to the Sanders campaign are the same ones who backed Obama in 2008. His campaign is banking on a similar coalition of young people, independents and first time caucus-goers to propel Sanders to victory.

Larry Kilburg, 64, of Bellevue, Iowa, said he planned to caucus for the first time for Sanders. "I think this year there's going to be a lot of newbies," he said.

In a direct appeal to Obama's Iowa coalition, Sanders says the same attacks Clinton is levying on him were tried on the president, too.

"Eight years ago Obama was being attacked. He was unrealistic. His ideas were pie in the sky. He did not have the experience that was needed," Sanders said. "But you know what, people of Iowa saw through those attacks then and they're going to see through those attacks again."

Fueled by his robust fundraising, Sanders has built a large organization in Iowa, with 103 paid staffers on the ground, as well as 15,000 volunteers, according to his campaign. But he got his foothold in the state later than Clinton, who has had professional staff in the state since last spring.

The Clinton campaign has not offered an official staffing number in the state in several months, but it is now well above the 78 paid people they said they had back in September. And the Clinton staff has been diligently knocking doors and organizing in cities and small towns.

Still, Sanders spokesman Michael Briggs said he was confident in the "enthusiastic workers and volunteers." A YouTube video released by Sanders' Iowa organization on how to caucus — with participants explaining the rules and acting out a mock caucus — has had over 61,000 views since Thursday.

Clinton and Sanders planned to spend most of the week leading up to the caucuses in Iowa, eager to parlay a win here into momentum heading into New Hampshire's primary. Sanders has built a solid lead in New Hampshire, while Clinton's campaign is banking on strong showings as the race heads toward states like South Carolina and Nevada that have more racially diverse populations.