Mitt Romney's flip-flop on gay rights has been questioned by Obama adviser David Plouffe.

Appearing Sunday on NBC's Meet the Press, Plouffe said Romney has “moved all over the place” on issues, including gay marriage.

During his appearance, Plouffe referred to a letter Romney wrote to gay GOP group Log Cabin Club of Massachusetts while campaigning for the U.S. Senate in 1994. In the letter, Romney claimed that he would a stronger advocate for gay rights than then-Senator Edward M. Kennedy.

Romney “has no core,” Plouffe told host David Gregory. “And everyday almost it seems to be we find another issue. He was supportive of doing things like cap and trade agreement, now he doesn't think that climate change is real. He was to the left of [the late Senator] Ted Kennedy on gay rights issues, now he wants to amend the constitution to prohibit gay marriage. He was an extremely pro-choice governor, now he believes that life begins at conception and would ban Roe v. Wade.”

“I can tell you one thing, working a few steps down from the president. What you need in that office is conviction. You need to have a true compass, and you need to be willing to make the tough calls. And you get the sense with Mitt Romney that, you know, if he thought it was good to say the sky was green and the grass was blue to win an election, he'd say it,” he added with a smile. (The video is embedded in the right panel of this page.)

Plouffe's comments come after Texas Governor Rick Perry and Obama strategist David Axelrod also criticized Romney's waffling on gay rights.