Former Rep. Barney Frank (D-Mass.) said the group urging Sen. Elizabeth WarrenElizabeth Ann WarrenWarren battles Carson: Housing discrimination 'the scandal that should get you fired' Overnight Regulation: Omnibus includes deal on tip-pooling rule | Groups sue over rules for organic livestock | AT&T, DOJ make opening arguments in merger trial Warren presses Mulvaney, Azar on tip pooling MORE (D-Mass.) to run for president is "a good thing."

"I think it's a good thing," Frank said of Ready for Warren in an interview with The Huffington Post. "It'll help keep liberal activity going and keep some pressure on people. But I think what's also very clear — if Hillary ClintonHillary Diane Rodham ClintonRepublicans invest nearly 0,000 in red Arizona district Al Franken: Sessions firing McCabe ‘is hypocrisy at its worst’ Papadopoulos encouraged by Trump campaign staffer to make contact with Russians: report MORE decides to run for president, she'll be the nominee."

Warren insists she is not considering a run for president, though her denials have not stopped some groups on the left from trying to draft her into the 2016 race.

Frank, meanwhile, has made clear his support for a Clinton candidacy, appearing in April at an event encouraging her to run. 

The former congressman has his name on the 2010 financial reform law, Dodd-Frank, which many liberals view as not going far enough. Warren has praised the law but also warned that it fails to solve the "too big to fail" problem for banks.

Warren has proposed a new Glass-Steagall law, which would prevent banks from doing both commercial and investment banking, but Frank emphasized that they agree on the Volcker Rule, which limits banks' ability to trade with their own money to seek a profit.   

"I think it's a matter of tone and culture," Frank said of the differences. "Even in Financial Services. Elizabeth's for Glass-Steagall; she also acknowledges that had Glass-Steagall still been in effect, it would not have stopped the crisis. There is this argument, 'Oh, banks are too big.' But there's overwhelming agreement on the reforms and on the regulation and on the Volcker rule. I don't see them as operational."

Frank, who returned to Capitol Hill this month to defend his namesake law in a hearing, also had some campaign advice for Clinton.

He said she would need "to explain why she voted for the war in Iraq and to reassure people that no, she's not ... for more of this or for staying in Afghanistan."

Clinton wrote in her new book, Hard Choices, that on the Iraq vote she "got it wrong."

"There was a period when people, Democrats, were told, 'You better vote for a war if you want to run for president,'" Frank said. "And fortunately, that has moved away."