Vice President Biden is greeted by Sen. Tom Harkin (D-Iowa) before speaking at Harkin's annual steak-fry fundraiser in Indianola, Iowa. (Charlie Neibergall/AP)

Iowa Democrats have often looked to Sen. Tom Harkin’s annual steak fry for a peek into the future of the party. On Sunday, Vice President Biden made clear he believes its future should be an extension of its present.

Biden, flirting with a third try at the presidency in 2016, delivered a muscular and impassioned defense of the policies and priorities of President Obama’s administration and offered a marker by which he said they should be judged.

“The president and I have had a laser focus on one thing: raising up the middle class,” Biden said, adding, “The measure of success of our administration will be whether or not the middle class is growing and the things that allow it to grow, and allow it to feel some security, are able to be put in place again.”

Speaking in a state with a strong antiwar tradition and where opposition to the use of military force in Syria is overwhelming, Biden said it was Obama’s leadership and determination to act that produced this weekend’s agreement with Russia to eliminate Syria’s chemical weapons.

“The president’s vision is absolutely clear,” Biden said. “He, in fact, is the reason why the world community is facing up finally — finally — to this hideous prospect of the largest stockpile in the world of chemical weapons being confiscated and destroyed.”

Vice President Biden and San Antonio Mayor Julian Castro, background, greet attendees at the Iowa event. (Steve Pope/Getty Images)

Sunday’s steak fry was billed as a showcase for two generations of Democratic leaders, and it turned out that the younger generation, represented by San Antonio Mayor Julian Castro, sounded just as enthusiastic about the present course as Biden.

Castro embraced Democratic history from Franklin D. Roosevelt through Lyndon B. Johnson to Obama, saying he believes in the blueprint that combines individual effort with the support of government programs.

“Our friends across the other side of the aisle say their blueprint is this: that if everybody will just go on their own, we’ll all be fine — if everybody will just do their own thing and government just leaves everybody alone, everything will be great,” Castro said. “But I believe in a different blueprint.”

Seven years ago, Obama came to this event as a freshman senator and stoked speculation that he might become a presidential candidate. Biden arrived Sunday knowing that it would fuel speculation about his political future, and he basked in his decades of relationships with Democratic activists in Iowa.

As he flipped steaks with Harkin and Castro, he enthusiastically embraced one person after another, prompting Harkin to say, “This is old home week for him.”

Biden arrived in Iowa — which holds the first-in-the-nation presidential caucuses — with expectations and questions about whether he will be a candidate in 2016, especially if former secretary of state Hillary Rodham Clinton enters the race, as her allies hope and expect.

In his 35-minute speech at the Warren County Fairgrounds, Biden made no mention of Clinton. He did, however, single out her successor, John F. Kerry, as “one of the best secretaries of state so far in the history of the United States of America.”

Biden presented himself as a progressive champion on social issues and took credit for giving the same-sex-marriage movement a significant push. It was only after Biden said last year on NBC’s “Meet the Press” that he was “absolutely comfortable with” the right of gay couples to marry that Obama embraced it.

“I know a lot of people criticized me for speaking out not long ago about gay marriage,” Biden said. “I could not remain silent anymore. It’s the civil rights of our day.”

Although many leading Democrats expect Biden or Clinton, but not both, to run, Harkin — who remained neutral in the 2008 primary contest that included Obama, Clinton and Biden — said it would be “pretty exciting” to see the pair in the 2016 race.

“Oh, my gosh,” Harkin said in an interview Saturday, “that would be a real contest. That would get a lot of juices flowing.”

Although he said he could envision the possibility of a newcomer with the “magic touch” he said Obama possessed here in the 2008 cycle, Harkin said this may be a time when Iowa Democrats look to someone with more experience as their standard-bearer.

“Is this going to be the election where people say, you know, ‘I think because of the times we need maybe someone who’s been tested, someone who has the experience, the background, the maturity, to take over the presidency’?” he asked.

In the interview, Harkin offered effusive praise for Biden as a possible president, saying he has “every ounce of ability.” And he noted the vice president’s longtime connection to this state and his diligence in maintaining contacts here. In Iowa, Harkin said, “he’s just Joe.”

As for Clinton, Harkin suggested that she take a page out of Obama’s 2008 playbook in Iowa. At one point, he said she was a “lousy organizer,” but then he pulled back, saying, “She just got out-hustled organizationally by Obama.”

“If there’s one thing I know about both the Clintons, they learn from past experiences,” Harkin said.

Although Biden and Castro were the headliners, the hundreds of activists who assembled here for the 36th annual steak fry were also celebrating Harkin’s long political career. Harkin, 73, who was first elected to the Senate in 1984, will step down at the end of next year, and he was praised by Biden and every other speaker as a progressive Democrat. Biden said he “changed America’s soul” as the champion of the Americans with Disabilities Act in 1990.

Harkin introduced Castro as one of the party’s rising stars and compared the response Castro received after his keynote address at the 2012 Democratic National Convention to the one Obama received at the party’s 2004 gathering. “Many people see this young man as the future of our party,” Harkin said.

Castro, who turns 39 on Monday, presented a contrast to Biden, who told reporters that he first visited Iowa in 1974, the year Castro was born. In his speech, Castro recalled how he and his identical twin brother, Rep. Joaquin Castro (D-Tex.), who accompanied him to Iowa, rose from poverty to attend Stanford University on scholarships and federal loans. He said they could not have achieved what they did on their own.

“I invested in myself,” Castro said, “but fundamentally I reached my dream because you invested in me, because the American people invested in me. That is America. That’s what’s great about this nation. That is the blueprint for success in the 21st century.”