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New Hampshire's Sen. Ayotte gives Romney key endorsement

By NBC's Jo Ling Kent and Garrett Haake 

Peterborough, NH -- Sen. Kelly Ayotte, R-NH, will endorse Republican presidential hopeful Mitt Romney Sunday at a rally in Nashua, the campaign told NBC News on Saturday evening. Her endorsement is the first by the three Republicans in New Hampshire's four-person Congressional delegation.

Alex Wong/Getty Images file

U.S. Sen. Kelly Ayotte, R-NH, will endorse Republican presidential candidate Mitt Romney, former governor of neighboring Massachusetts.

This is an important endorsement for Romney, who has also been formally backed by John Sununu, former New Hampshire governor and White House chief of staff, and former Sen. Judd Gregg, R-NH.

Ayotte, 43, is considered a well-respected rising star in the Republican party. She won a closely fought GOP primary for the senate seat in 2010. Earlier, she was reappointed New Hampshire attorney general by Democratic Gov. John Lynch after first being appointed by Republican Gov. Craig Benson.

Ayotte is the sixth sitting senator to announce support for Romney, and the second to do so just this week.

In an email to supporters, Ayotte said she is endorsing Romney as a candidate "who can win." She cited his electability and private sector experience, calling Romney the "strongest candidate to face President Obama."

Ayotte also committed to joining Romney on the trail in the first-in-the-nation primary state, similar to New Jersey Gov. Chris Christie's promise to Romney.

"I will be working as hard as I can to help him secure the Republican nomination," Ayotte told voters late Saturday evening.