Washington (CNN) - A senior Democratic source involved in Chris Dodd's campaign tells CNN that Democratic party officials had become convinced that Dodd's Connecticut re-election race was "virtually unwinnable for us."
Still, while this source and others admit there have been quiet conversations among party officials for some time about Dodd stepping aside, they say it does not appear that party leaders specifically asked him to do so.
"People have too much respect for Chris Dodd to try to get him out of this race," said the source involved with his campaign. "He had to come to it on his own."
Another source close to Dodd tells CNN he had been well aware of his uphill battle for months. This source concedes that the political reality was a big part the reason he decided not to seek re-election, but insists "this isn't a decision forced upon him or by anyone. He was looking at his career, looking at his record of accomplishments over the past 35 years, asking what else is there."
An internal Dodd campaign poll taken last month showed him trailing the leading Republican contender for his seat, Rob Simmons, 46-51 percent, in the Democratic-leaning state - where the same poll indicates President Obama holds a high favorability rating.
The source close to Dodd says his recent personal tragedies and challenges also weighed heavily in his decision to retire. He was diagnosed and treated with prostate cancer this summer, and also lost his sister and best friend, Ted Kennedy, to cancer in the span of three weeks.
"At a certain point he asked himself 'Why am I running? Why put myself through this? He looked back and said 'I've already done a hell of a lot," said the source close to Dodd.
Democratic sources say Dodd began making calls to associates about his decision Tuesday. However, a source with knowledge of the conversation tells CNN that he did not call Senate Majority Leader Harry Reid until after midnight Eastern time, after the news had already been reported.
Despite what many Democratic sources call widespread respect for Dodd, it was hard for party strategists to hide their happiness with his decision, since it clears the way for Connecticut Attorney General Richard Blumenthal to run. He is a popular, long-serving figure who Democrats believe has a good chance of keeping the seat in their column.
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"It's not a cakewalk, but it turns that race from a very uphill - pushing a boulder up a cliff - to a race that is very much winnable," said a senior Democratic strategist.
At his formal announcement Wednesday, Dodd - whose father, former Connecticut Sen. Thomas Dodd, lost his own re-election bid in 1970 - will have his wife Jackie, children and extended family on hand.