"If he enters this race, Jeanne will immediately become the top target of Karl Rove and the Tea Party Super PACs," Gillibrand wrote in the fundraising email sent out on Friday. "Jeanne needs our help now to prepare for the attacks from Brown and his allies. They’ve launched a 'Granitebomb' campaign to fight back."

Less than 24 hours earlier Brown was asked about a possible campaign in New Hampshire. Shaheen is up for reelection in 2014.

"I don't think I'm done with politics, but I'm not going to rule out anything right now because I really haven't thought a heck of a lot about it," Brown said, according to CNN.

In her fundraising email, Gillibrand described Brown, who lost reelection to now-Sen. Elizabeth WarrenElizabeth Ann WarrenGovernment watchdog finds safety gaps in assisted living homes David Crosby: Shared dislike for Trump could reunite Crosby, Stills, Nash and Young Dem senators tell Trump he doesn’t have ‘legal authority’ to launch preemptive strike on North Korea MORE (D-Mass.) in 2012, as a "billionaire-backed Republican."

"You read that right: A billionaire-backed Republican from Massachusetts who voted against equal pay and critical job-creation bills wants to take on Jeanne ShaheenCynthia (Jeanne) Jeanne ShaheenSenators call for probe into US Olympic Committee, USA Gymnastics after abuse scandal Trump officials take heat for declining Russia sanctions Schumer to Trump administration: Who met with Putin's spy chief? MORE – a tremendous champion for our progressive values," Gillibrand writes in the email.

"Brown raised $37 million in 2012 and spent it on partisan negative attacks against Elizabeth Warren."

Gillibrand's goal in the email is to raise a total of $100,000 to "send a message to Scott Brown and his Tea Party allies that we have [Shaheen's] back."