Vice President Biden rallied Democrats at Sen. Tom HarkinTom HarkinThe Hill's 12:30 Report Distance education: Tumultuous today and yesterday Grassley challenger no stranger to defying odds MORE’s (D-Iowa) annual fundraiser in Iowa on Sunday, in what could be the first step in exploring a potential 2016 presidential bid. 

The 36th annual steak fry has historically been headlined by leading Democrats interested in leaving a footprint in Iowa, the first state to hold presidential caucuses. In his address, Biden paid tribute to the retiring Harkin, who is one of the few lawmakers on either side of the aisle to have a longer tenure in Washington than the vice president.

“There’s not a whole lot of people that I’ve served with, and there’s only 13 people in American history that have served longer than me in the United State Senate, so I’m told, there’s not a whole lot of people that I know who have the character, the conviction and the conscience of Tom,” Biden said, according to a media pool report.

The event sought to raise funds for a committee Harkin runs that supports Democratic candidates, and in his address, Biden stressed how important it will be for Democrats to hold onto Harkin’s seat.

“Unless we can maintain this seat, unless we can begin to break down the majority in the House of Representatives, everything you have fought for for the last six years and beyond is in jeopardy,” he said. “This is now a party where the tail is wagging the dog, where [Sen.] Ted CruzRafael (Ted) Edward CruzTexas Republicans slam White House over disaster relief request Dem rep: Trump disaster aid request is 'how you let America down again' Moore endorsements disappear from campaign website MORE [R-Texas] is running the show, a freshman, in terms of the ideas of the party.”

Biden has expressed interest in running for the Democratic presidential nomination in 2016, and political watchers are debating whether the vice president would challenge former Secretary of State Hillary ClintonHillary Diane Rodham ClintonO’Malley tells Dems not to fear Trump FBI informant gathered years of evidence on Russian push for US nuclear fuel deals, including Uranium One, memos show Pelosi blasts California Republicans for supporting tax bill MORE (D), the party’s unquestioned front-runner, if she commits to seeking the nomination.

San Antonio Mayor and rising Democratic star Julián Castro was the other featured guest at the event. In an interview with The Washington Post ahead of the fundraiser, Castro said he hopes the two “work it out” before the Democratic primary.

“Of course, my hope, like most Democrats, is that folks work that out however they work that out,” he said. “There’s always a benefit, some benefit, when you have two strong voices, but I believe at the end of the day, Democrats will have a standard-bearer that everybody can get behind. It’s very early on right now. We don’t know whether Secretary Clinton or the vice president will run at all. But if you’re asking if we should have a primary fight or not — of course not. I hope they work it out.”