Robinson appears to have turned in at least 10,073 certified signatures to local city and town clerks, according to Secretary of State William Galvin.

Despite having crossed that line, Robinson's fight may not be over, Galvin said. Some of those signatures could be disqualified once Robinson collects them and turns them into the state.

They could also be challenged by rivals hoping to knock Robinson off the ballot.

"I have not seen a single signature. When they come in here, there may be technical problems," Galvin said. "The indication from the clerks is that there appears to be 10,073 signatures, but I can't say whether he'll be on the ballot."

Robinson called the latest signature total a vindication against those naysayers who predicted he would not break the 10,000 mark. Robinson said he turned in about 13,000 signatures.

"We never lost faith. We knew we would pull it off. We knew it would go down to the wire, but we never wavered," Robinson said Monday.

Robinson also dismissed the possibility of a challenge to those signatures by either of the other candidates running for the seat: Kennedy, a Democrat, and Libertarian Carla Howell.

Signatures can be challenged for a number of reasons ranging from the signer's party registration -- only registered Republicans or independents can sign Republican papers -- to questions about whether the signer truly lives at the address given.

Kennedy has "no plans to challenge" any signatures and would not comment on a possible Robinson campaign, according to Kennedy spokesman Will Keyser.

Carla Howell's campaign will study Robinson's signatures if he is slightly over the 10,000 mark and if no one else does, according to Michael Cloud, CEO of Howell's campaign.

Cloud said he believes some of Robinson's signatures might have been certified after the May 9 deadline and should be disqualified.

"If he has any illegal signatures, we would challenge illegal signatures," Cloud said. "If he's just a few signatures over, he's in trouble."

Robinson said he has hired a lawyer to fend off any challenges.

"Why would anyone want to keep us off the ballot? What are they are afraid of?" Robinson said.

Both Howell and Kennedy have more than enough certified signatures to guarantee themselves a place on the ballot, Galvin said.

Robinson sent a letter to Galvin's office Monday saying he wanted to inspect the signatures disqualified by the local clerks to see if any of those signatures should be reinstated.

Robinson said he has identified up to 1,000 disqualified signatures he wants reconsidered.

Robinson's campaign has been plagued by controversy from the start. Top Republicans, including Gov. Paul Cellucci, at first embraced the campaign and then withdrew their support after Robinson revealed embarrassing details of his past.

In the 11-page "Robinson Report," Robinson outlined a drunken-driving arrest -- he was eventually cleared -- and a relationship with a girlfriend who took out a restraining order against him.

Robinson said he spent $100,000 of his own money to gather the signatures. He has accused Republican Party activists of trying to thwart his campaign.

If Robinson fails to get on the ballot it will mark the first time since 1916, the year United States senators began being popularly elected, that a Massachusetts Democratic Senate candidate will run without Republican opposition.