In a speech announcing his bid, Rubens slammed Shaheen as a "career politician and party rubber stamp."

“We cannot wait another six years to give this Senate seat to a person with the bravery, the energy and the independence to say, ‘hell, no’ to business as usual in Washington, a senator willing to face controversy, cut through gridlock and build support for solutions to our nation’s big, pressing challenges," he said, according to the Concord Monitor.

Rubens is likely to face a challenge in the primary from former Rep. Charlie Bass, who would enter the race the frontrunner, and conservative activist Karen Testerman, both of whom have indicated they're exploring a bid.

Former Sen. Bob Smith and former Massachusetts Sen. Scott Brown have also indicated they're interested in running, but Smith lives in Florida and Brown calls Massachusetts his home, so their bids look less likely.

Rubens' first day of campaigning was overshadowed by a blog post he wrote in 2009 that suggested more women in the workplace led to a rise in violence perpetrated by men.

“The collaborative, flexible, amorphously-hierarchical American economy is shutting out ordinary men who were once the nation’s breadwinners in living-wage labor and manufacturing jobs,” he wrote, according to BuzzFeed, which first unearthed the post. “Because status success is more vital to the male psychology, males are falling over the edge in increasing numbers.”

In later interviews, Rubens defended the post, saying he was more addressing the detrimental effects economic change has had on men rather than focusing on women in the workplace.

Rubens is more moderate than most Republicans. He supports same-sex marriage and abortion rights, and favors a carbon tax, a profile that will serve him well in New Hampshire, which leans largely libertarian on social issues.

But Democrats were already pointing to his blog post as evidence he's "wildly out of touch with New Hampshire families."

“New Hampshire GOP’s latest Senate hopeful has a perspective on women in the workplace that reveals he is wildly out of touch with New Hampshire families, New Hampshire values and also reality,” said New Hampshire Democratic Party spokesman Harrell Kirstein. “A self-described moderate on social issues, state Sen. Jim Rubens has set a new bar for insulting women. New Hampshire voters will reject his twisted logic as they have with the backward Republican agenda.”