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Former Secretary of State Hillary Clinton may be headlining Sen. Tom Harkin's annual Steak Fry today, but the longtime progressive senator indicated that shouldn't be taken as an endorsement should she decide to run for president in 2016.

Harkin, who is retiring after 30 years in the Senate and was hosting his last annual Steak Fry today, said progressives should raise questions about Clinton's foreign policy and economic positions.

"As someone who has carried the liberal, progressive populist banner for many years, we're always nervous about people moving too far to the right," Harkin told ABC News' Jonathan Karl for "This Week." "See we, a lot of us believe the center ought to be moved back, that the center has moved too far right."

ABC News

PHOTO: Senator Tom Harkin (D) Iowa on 'This Week'

Asked where Clinton's positions fell on the political spectrum, Harkin responded, "Well, I don't know, I mean I think this is something that will be developed and we'll find out when, if she, if she decides to run. You know, what's her vision for America?"

When asked if he had "real questions" about Clinton's stances on issues, Harkin said, "I do about everybody" considering a run for the White House.

He added that President Barack Obama's positions have been less progressive than he had hoped they would be.

"I must be frank with you, I thought Barack Obama was a great progressive and a great populist and quite frankly, I haven't, some things have happened that I don't agree with," Harkin said.

And while most eyes on Clinton this weekend are reading signs for what her return trip to Iowa means for her 2016 presidential prospects, Harkin said Clinton's trip will have more impact on the 2014 midterm elections, as she and former President Clinton begin hitting the campaign trail for Democrats facing tough election battles.

Read more here:
Progressives Want to See Clinton's 'Vision for America'