Dick Gephardt (search) stepped up his criticism of Howard Dean (search) on Thursday, arguing that his chief rival for the Democratic nomination favored deep cuts in health programs and bad trade policies.

Gephardt said Dean would have pushed through cuts in Medicare (search) costing average taxpayers thousands of dollars and would have backed trade policies that have sparked "a race to the bottom."

"When I am president, that just will not happen," he said. "To me, there is nothing more shortsighted than trying to balance the budget by cutting Medicare. I am going to protect Medicare, and Republicans will succeed in cutting it over my dead body."

In stop after stop across northern Iowa, Gephardt hammered home differences with Dean that he underscored in a speech Wednesday designed to define his candidacy.

Gephardt was matching that criticism with a new television commercial bashing Dean on the Medicare issue, saying it's important for the rivals to spell out differences for activists looking toward Monday's caucuses.

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Polls have shown the race very tight, with Dean and Gephardt bunched together at the top and John Kerry and John Edwards increasingly part of the picture. All of the top-tier candidates were working overtime to energize backers and turn them out for the caucuses.

Iowa Sen. Tom Harkin, who last week endorsed Dean, quickly rode to his defense.

"This is just nonsense," said Harkin. "If there was anything to that charge, I couldn't have supported Howard Dean."

Gephardt sought to use trade and Medicare to enliven backers in labor and other key constituencies, warning that Dean "enthusiastically supported" trade deals that he said have shipped thousands of American jobs overseas

"What I say is, a good trade deal or no trade deal," he said as he cited squalid working conditions in many foreign countries. "These people live in worse conditions than many farm animals in Iowa."

Gephardt rejected suggestions that being strident reflects worries that Dean has edged ahead of him in the must-win caucuses.

"At the end of the day, this is an organizational challenge," he said. "We have the best organization."