In Concord today, Sen. Judd Gregg will endorse ex-MA Gov. Mitt Romney's presidential campaign, Republican sources with knowledge of the endorsement said.

Gregg is the ranking Republican on the Senate budget committee, a former Governor of New Hampshire and one of its Senators since 1992, endorsed George W. Bush in 2000.

Gregg has been a quiet fan of Romney's since the former governor began to seriously think about running for president, but he's remained publicly neutral. Many of his senior aides and advisers have joined Romney's campaign.

It's tough to say that any endorsement carries votes these days, but Gregg's ability to validate Romney's competence and economic message, as well as his freedom to act as a surrogate for Romney at events should not be underrated.

Romney will officially file his paperwork to enter the New Hampshire primary at noon:30 ET. That's when Gregg will endorse him.

The news overshadows a major push by Rudy Giuliani in the state. The former mayor is spending four days there this week, his longest stretch of campaign time to date.

New Hampshire's other Senator, John Sununu, has said he'll remain neutral for the primaries.

Update: the Union Leader has this too.

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