Democratic presidential candidate John Kerry (search) blasted President Bush and the economy Thursday, questioning Bush's motives for war in Iraq and blaming him for a sluggish return to economic growth.

''If there's one person in this country who ought to be laid off, it's George Bush,'' Kerry said.

The stinging attacks appear to be working. The Massachusetts senator has catapulted to the front of the Democratic field and is now the undisputed front-runner in New Hampshire's first-in-the-nation primary, according to the latest poll.

Kerry is also running even in a first-place tie nationwide with Sen. Joe Lieberman (search). The two top-tier candidates are the only ones running in double digits, at a tie of 15 percent, according to the latest Fox News-Opinion Dynamics poll. 

Lieberman, who topped national polls for months largely on the strength of his name recognition as former Vice President Al Gore's (search) 2000 running mate, has dropped four points since May. Kerry has gained three points, and appears to be taking the wind out of the sails of Missouri Rep. Dick Gephardt (search), who has dropped from second to third and seen his support plummet 50 percent in one month, from 14 percent to 7 percent.

With the added boost, he has begun to sharpen his attacks on Bush to short declarations.

"Surpluses blown! Deficit up! Jobs down!" he yelled.

Bashing Bush has become a regular part of the senator's New Hampshire swing. On Wednesday night, Kerry declared that Bush broke a pre-war promise to build international support before attacking Iraq, and then waged war based on questionable intelligence.

"He misled every one of us," Kerry told about 250 people in a downtown Lebanon park. "I will not let him off the hook throughout this campaign with respect to America's credibility and credibility to me because if he lied, he lied to me personally."

The "if" on the end of Kerry's attack appears designed to split the difference between two camps in the Democratic field. On one hand, former Vermont Gov. Howad Dean and Florida Sen. Bob Graham accuse the president of deception. On the other hand, Lieberman, Gephardt and North Carolina Sen. John Edwards (search) have withheld judgment until a congressional review is complete. Kerry, who voted in support of war, said he would like to see what congressional investigations uncover.

In the latest New Hampshire poll, Kerry has the biggest lead among likely independent and Democratic primary voters — 10 percentage points over Dean, with Lieberman and Gephardt the only other candidates to break double digits. Still, 23 percent are undecided.

But emerging as an early front-runner can be a mixed blessing. It helps with fund-raising and media coverage, but the Kerry camp knows it can also flatline and face a backfire in New Hampshire because of the state's legendarily fickle voters, who have a long history of building up early favorites only to knock them down on primary day.

Fox News' Carl Cameron contributed to this report.