Updated

Democratic Sen. Joe Lieberman is enlisting help in his re-election campaign from former President Clinton, the man he criticized in 1998 for "disgraceful behavior" in a sex scandal with a White House intern.

Clinton and Lieberman are scheduled to campaign together in Connecticut on Monday as the three-term lawmaker struggles against challenger Ned Lamont, a multimillionaire businessman who has questioned his rival's Democratic credentials and assailed his support for the Iraq war.

A new poll released Thursday showed that Lieberman has lost ground to Lamont and is narrowly trailing him for the first time in their race. Lamont had support from 51 percent and Lieberman from 47 percent of likely Democratic voters in the latest Quinnipiac University poll — a slight Lamont lead given the survey's error margin of plus or minus 4 percentage points.

The primary is Aug. 8 — summer vacation season — when turnout in Connecticut primaries is typically about 25 percent of registered voters.

Lieberman is arguably the most vulnerable incumbent senator in a primary. Sens. Daniel Akaka, D-Hawaii, and Lincoln Chafee, R-R.I., face viable opponents in September contests. Sen. Marie Cantwell, D-Wash., has secured the support of some of her early Democratic foes.

Liberal blogs and Democratic activists have targeted Lieberman — and lifted Lamont's political fortunes — for his stand on the war and perceived closeness to President Bush. He also upset some Democrats with his plan to run as an independent if he loses the primary.

Several Senate colleagues, among them Democrats Barbara Boxer of California and Ken Salazar of Colorado, plan to campaign for Lieberman in Connecticut. Clinton, however, is the party's rock star as well as the one who would revive talk of interns and impeachment.

In September 1998, as the scandal raged, Lieberman was the first prominent Democratic lawmaker to openly criticize Clinton's conduct with former White House intern Monica Lewinsky. On the Senate floor, Lieberman spoke about being "personally angry because President Clinton had, by his disgraceful behavior, jeopardized his administration's historic record of accomplishment."

The senator said his personal dismay evolved into "a larger, graver sense of loss for our country, a reckoning of the damage that the president's conduct has done to the proud legacy of his presidency."

Two years later, Al Gore selected Lieberman to be his running mate on what turned out to be the losing Democratic ticket. In 2004, Lieberman made an unsuccessful bid for the party's presidential nomination.

At a news conference Thursday, Lamont said he was "a big fan of President Clinton" and the world would have been a different place if he had been allowed to serve a third term.

"But that said, a lot of testimonials from folks coming up from Washington aren't going to make a difference," said Lamont, who continued to focus on Iraq.

"If President Clinton was president in 2003, do you think he would have had a unilateral invasion of Iraq with no allied support and no support from the neighbors?" he asked.

With less than three weeks to the primary, Lieberman has hired Washington, D.C., strategist Tom Lindenfeld to oversee a get-out-the-vote effort. Lindenfeld helped to organize such an effort for Clinton's 1992 presidential campaign.

"Probably for Lieberman, the best thing he can do right now is get out his troops," said Douglas Schwartz, director of the Quinnipiac University Poll. "This is going to be about turnout right now."

Marion Steinfels, Lieberman's campaign spokeswoman, said volunteers are coming from out of state to help.

Leading Democrats in the Senate — Hillary Rodham Clinton of New York and John Kerry of Massachusetts — have said they would back whoever wins the primary.

Despite the close primary race, the new poll provided some good news for Lieberman. In a three-way race, the senator would prevail.

The poll found that among all registered Connecticut voters, including non-Democrats, Lieberman had the support of 51 percent, followed by Lamont with 27 percent and Republican Alan Schlesinger with 9 percent.

The telephone survey of 2,502 registered voters, 653 of them likely Democratic voters, was conducted July 13-18. The margin of error for the overall survey was plus or minus 2 percentage points.