“I think it’s shameful for her to do that, for one, because I’m not a declared candidate,” Brown said after a fundraiser in New Hampshire, according to The Boston Globe. “I think she should be addressing the government shutdown problem.”

Brown is rumored to be considering a run for Senate in New Hampshire, and recently sold his home in Massachusetts, sparking fresh speculation that he's looking at a bid.

Shaheen warned supporters that Brown could could challenge her in a Friday fundraising email that called Brown's recent visit to New Hampshire “his latest hint at running against me.”

The former Massachusetts Senator's trips to both New Hampshire and Iowa have fueled speculation that he may in fact be considering a presidential run. And though he decided against running for governor in Massachusetts, he hasn't ruled out a run for another elective office.

He demurred when asked where he was in the decision-making process.

“I’m doing exactly what I said I was going to do,” Brown said, “which is traveling around the country helping other committees, individuals and groups raise money and raise awareness and try to get my message of problem solving.”