With the latest poll showing a dead heat between his fellow Democrat Martha Coakley and Republican Scott Brown, Clinton told voters they had the choice between a candidate who would be the 41st GOP vote to uphold a filibuster in the Senate, or the 60th Democratic vote to pass President Obama's health care overhaul and other legislative priorities.
"You just have to decide if you want to pick the person who gets to shut America down," Clinton said. "I thought Massachusetts was about leading America into the future."
"There is a mass national effort to discourage progressive independents from voting and to discourage disappointed liberals from voting," he said.
With polls all over the place, Clinton said, it's hard to predict whose supporters will show up in greater numbers on Tuesday — Coakley's, or those of her Republican opponent, state Sen. Scott Brown.
The opulent, sweltering room at the Copley Plaza Hotel was filled to capacity with Coakley's supporters, many of them worried about the outcome of Tuesday's race.
Sen. John Kerry told the crowd of 750: "The vote here will determine the balance of power in America."
Kerry accused Brown of staging an "extraordinary camouflage campaign" concealing his conservative positions with moderate slogans.
And he lashed out at the GOP, saying it had decided to incite voters.
"They made a calculated political decision that they would say no to governance, create anger and then let the anger fall on those who are struggling to make the choices of these tough decisions. And now they have the gall to want to receive a bonus for doing it," Kerry said.
"Well, my friends, the only things the Republicans say 'yes' to are Rush Limbaugh, Glenn Beck, the Tea Partiers and Fox News."
Kerry took the stage with the aid of the silver-tipped cane Kennedy used before he died in August of brain cancer. Kennedy's widow, Victoria Reggie, lent it to Kerry as he recovers from hip-replacement surgery.
Boston Mayor Thomas Menino also tried to elevate the stakes of Tuesday's election, noting the effect of electing a Republican counterweight to Kerry.
"You don't want somebody down there who'll negate every vote that John Kerry takes, do you?" the mayor said.
A Suffolk University poll released Thursday showed Brown with 50 percent and Coakley with 46 percent, a statistical tie but far closer than the 15-point lead the Democrat enjoyed just last weekend.
A third candidate, independent Joseph L. Kennedy, unrelated to the late senator, is also running in Tuesday's special election. He received only 3 percent of the vote in the Suffolk survey.
The Associated Press contributed to this report.
This program aired on January 15, 2010. The audio for this program is not available.