Former Tennessee congressman Harold Ford Jr.said Monday he won't challenge Sen. Kirsten Gillibrand in this fall's Democratic primary because he doesn't want to divide and weaken the party.

In a New York Times op-ed posted online for Tuesday's editions, Ford said he believed he could have won but didn't want to risk a bitter primary that could help a Republican take the seat.

"I've examined this race in every possible way," Ford wrote, "and I keep returning to the same fundamental conclusion: If I run, the likely result would be a brutal and highly negative Democratic primary - a primary where the winner emerges weakened and the Republican strengthened."

Ford moved to New York after losing the 2006 U.S. Senate race in Tennessee, taking a job with Bank of America Merrill Lynch. He had spent the past seven weeks traveling the state and meeting with voters, Democratic dignitaries and elected officials to gauge support for a potential campaign.

Many in the Democratic establishment backing Gillibrand, including the White House and New York Sen. Charles Schumer, sought to discourage Ford from running. In Ford's op-ed, he complained of the party's "campaign to bully me out of the race," claiming it showed Democrats are nervous.

Gillibrand, who was appointed to her seat last year when Hillary Rodham Clinton became U.S. secretary of state, ignored Ford when he first declared he was testing the waters. But after Ford began regularly challenging her, the race that was not yet a race quickly turned ugly.

Ford called Gillibrand various names, including a hypocrite, a liar, an unelected senator and a parakeet who takes positions based on whatever party leaders tell her to do.

Gillibrand sought to paint Ford as a wealthy carpetbagger who cares only about his Wall Street friends and has tried to hide the conservative streak that made him popular in Tennessee.

As a congressman, Ford described himself as "pro-life," said illegal immigrants should be deported if caught and voted for a constitutional amendment to define marriage as a union between a man and a woman.

Gillibrand spokesman Glen Caplin said that no matter who her opponent is this fall she would "wage a vigorous campaign on her strong record and her vision for New York."

The news about Ford was greeted with relief by some Democrats who feared a protracted primary battle would leave them vulnerable to a Republican challenge in November. State party chairman Jay Jacobs said Ford "sacrificed his opportunity for the greater good."

"I'm very pleased that he made that decision," Jacobs said. "I had stressed to him we need the Democratic party unified."

Those believed to be considering runs on the GOP line include real estate tycoon and Daily News publisher Mortimer Zuckerman and former George W. Bush administration adviser Dan Senor. Attorney Bruce Blakeman has declared his candidacy.

Ford would have faced the challenge of running without wide support from New York's Democratic power brokers.

Gillibrand has spent months lining up endorsements from labor unions, politicians and interest groups crucial to Democrats running statewide races. She has been endorsed by leaders of 59 of New York's 62 county party organizations, including those in Democrat-heavy Manhattan and the Bronx.

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Associated Press writer Michael Hill contributed to this story from Albany.

(Copyright 2010 by The Associated Press. All Rights Reserved.)