Seth Moulton, the Marine veteran eyeing an independent bid against Rep. John Tierney (D-Mass.), said he is being encouraged to run for Congress by notable Massachusetts Democrats, many of whom are worried about holding the district.

“Obviously, they’re concerned that Tierney’s going to lose the seat,” he said. “This wasn’t Republicans who asked me to do this, this was Democrats.”

Moulton declined to say who these Democrats were, but he specified that none were associated with the formal party apparatus in the state or in Washington, D.C.

He said he hasn’t yet made a decision yet on a run but is “seriously” considering it. If he were to run, he would have to gather and file 2,000 signatures by the end of the month to get on the ballot.

Moulton said he would caucus with Democrats if he is elected. “I’m fairly centrist,” he said. “I think there’s a good argument that we need more of that in Congress. But I’m not a political type, I’m very much an outsider”

The national and state Democratic establishment are publicly continuing to strongly back Tierney, whose campaign shrugged off the news of a potential new challenger.

“Anyone is definitely welcome to participate in the Democratic process,” Tierney spokesman Grant Herring said in an email. “We are confident that John Tierney will win this race.”

Moulton, who received his undergraduate degree from Harvard University in 2001, served four tours of duty in Iraq. He received a joint master’s degree in 2011 from Harvard’s Kennedy School of Government and Harvard Business School. He works for a privately backed effort to bring high-speed rail service to the U.S.

Tierney already faces a tough campaign for a ninth term against Republican Richard Tisei, who raised an impressive $569,000 in the second quarter of this year. Tisei, a former state Senator and GOP nominee for lieutenant governor in 2010, ended June with $803,000 in cash on hand.

Tierney’s campaign hadn’t finished its fundraising tally for the quarter as of Wednesday afternoon. But the Congressman ended March with $795,000 in cash on hand. Tisei outraised Tierney in both the fourth quarter of 2011 and the first quarter of 2012.