It started last Monday.

A week after the deadly bombings at the Boston Marathon, Democratic Reps. Ed Markey and Stephen Lynch resumed their Massachusetts Senate campaigns in earnest. There was a debate that night, and the first question was about the attack.

And since that time, the stretch run of the Democratic race has been consumed by a back-and-forth over homeland security that has persisted for a week.

Markey, with the Democratic establishment behind him, appears to have held his front-running position as the two candidates have traded blows in the final stage of what had been a mostly cordial campaign. He heads into Tuesday's election as the favorite to win the Democratic nomination.

Lynch made the first move at the Monday debate, sparking an exchange on homeland security. By Friday, he was playing defense, as holes in the validity of one of his claims prompted questions about his argument.

"What specific changes would you pursue in our domestic and foreign policies to make us safer?" asked the Boston Globe’s Cynthia Needham, one of the debate's two moderators.

"I think one of the stark differences between myself and Mr. Markey is our voting record on homeland security," Lynch said in his response to the question. Lynch went on to slam Markey for voting against a joint terrorism task force, a group he said "enabled our response" to the Boston bombings. He touted his own support for the measure.

“You can say you wrote this and wrote that. I understand policy,” Lynch said. “But when the issue came up to create that joint task force, I voted yes, you voted no. I don’t know how you spin that.”

Twenty-four hours later, the sparring continued in a second debate. Markey, noticeably feistier than he was the previous night, countered Lynch's attack with a charge his opponent was using "Karl Rove swiftboat" tactics to smear his record. Markey also sought to cast doubt about Lynch's votes, asking him, “who were you standing up for when you cut all that homeland security money?”

By Friday, Lynch's argument against Markey regarding the task force was blunted by a local report. The Boston Globe reported that Boston's Terrorism Task Force was created years before Lynch was even in Congress. From the Globe story:

Boston’s Joint Terrorism Task Force was created in 1997, an FBI spokeswoman said. That was four years before Lynch was sworn into ­office. And it was not crafted by ­Congress, said Tom Powers, a former FBI agent who helped create it...
On Monday, Lynch’s campaign ­attempted to bolster his argument by pointing to a July 2002 vote in which the two candidates parted ways. Lynch voted yes and Markey voted no for a piece of legislation that, when it became law, gave the secretary of homeland security the authority, though not the mandate, to create a Joint Interagency Homeland Security Task Force.
But that Task Force is not Boston’s Joint Terrorism Task Force, the group that led the hunt for the Marathon bombers.

Markey's campaign says Lynch "shamefully" questioned Markey's commitment to the nation's security in the wake of the bombings.

"Stephen Lynch resumed his campaign after a terror attack on Boston by shamefully questioning Ed Markey's commitment to keeping America safe, and falsely accusing him of opposing the task force that responded to the Marathon bombings," said Markey spokesman Andrew Zucker.

"There was still a vote on a task force, and Markey voted no," Lynch spokesman Conor Yunits said.

Lynch's strategy has been to elevate the issue of national security during the final week of the race. He also ranTV ad thanking authorities and first responders for their reaction to the marathon bombings.

Markey, on the other hand, seems mostly content to run out the clock by keeping up the positive message he was sticking to before the attacks. But he too has been pitching himself on homeland security. A recent ad touts his support for spearheading a measure to ensure cargo screening after the Sept. 11, 2001 attacks. Markey also has been airing ads about women's issues and his Globe endorsement.

Turnout is another factor the marathon bombings might affect in the Democratic race. It's difficult to predict turnout in special elections, and even more so in this particular case.

Lynch has been sidelined by illness during the final day of the campaign, his spokesman said Monday morning. The congressman has canceled most public events.

On the Republican side, former Navy SEAL Gabriel Gomez and former U.S. Attorney Michael Sullivan are the two front-runners. The Democratic nominee will begin the general election campaign as a substantial favorite.