In the hours and days following his re-election win, Senate Minority Leader Mitch McConnell (R-Ky.) fielded dozens of congratulatory calls and reached out to Democratic and Republican lawmakers, as well as President-elect Barack Obama.

But despite a previously solid working and personal relationship with his Democratic counterpart, McConnell chose to ignore both the election night call and a subsequent follow-up call from Majority Leader Harry Reid (D-Nev.), whose party had dumped more than $6 million into Kentucky in an ultimately futile push to knock off the Republican leader.

In fact, according to Democrats and Republicans familiar with the situation, while McConnell and Obama spoke on the Thursday following the election, it took McConnell some nine days to ultimately respond to Reid’s overtures.

Republicans warned that Reid should be prepared for a full-court press during his own 2010 re-election bid, and that the sudden deterioration in relations, no matter how short-lived, is a direct result of what they view as an overly aggressive Democratic effort to unseat McConnell.

“The Majority Leader made a tactical error that could potentially cost him his job when he signed off on $6 million of attack ads the last few weeks in Kentucky. McConnell never takes political attacks personally, but he is someone who has never hesitated to repay his opposition for their courtesy,” a senior Republican official said, adding that identifying a high-quality opponent to challenge Reid will be a priority for the party in the coming months.

The depth of the rift between the two longtime colleagues is unclear — both lawmakers pride themselves on maintaining a certain amount of personal distance from the stresses of their jobs; publicly, neither side is acknowledging the sudden coolness to a once-warm relationship.

McConnell spokesman Don Stewart declined to comment except to say that “Sen. McConnell is not targeting Sen. Reid.”

Reid spokesman Rodell Mollineau denied any significant divisions exist between the two leaders and said Reid expects to continue to work with McConnell.

“Sen. Reid has a good working relationship with Sen. McConnell, and he expects that to be the case in the 111th Congress,” he said.

Mollineau also dismissed much of the talk of bad blood as simply a way for Republicans to justify going after Reid aggressively over the next two years.

“I’m not sure why Senate Republicans are going out of their way to justify why they’re going to be attacking Sen. Reid in 2009 since they’ve been doing it since he became leader in 2004,” Mollineau said.

But privately, Republicans said Reid and Democratic Senatorial Campaign Committee Chairman Charles Schumer (N.Y.) went above and beyond traditional campaign efforts, and they added that it became clear in the closing days of the campaign that Reid was actively involved in the national effort to oust McConnell.

One Republican points to the comments made by Schumer during a pen-and-pad press conference with reporters just before the election, when Schumer seemed to acknowledge that he and Reid had coordinated on the DSCC’s $6 million push in Kentucky. “Harry Reid and I discussed this, and there had been rules of etiquette. … The rules of etiquette were broken with [former South Dakota Democratic Sen.] Tom Daschle,” Schumer said.

Daschle’s 2004 race has loomed over Reid and McConnell’s relationship since Reid replaced Daschle as Minority Leader following his defeat.

Daschle and Reid had a close professional and personal relationship, and the decision by Republicans to dump millions into now-Sen. John Thune’s successful race against him — and to have then-Majority Leader Bill Frist (R-Tenn.) travel to South Dakota to campaign for Thune — angered Reid and other Democrats.

Although as Schumer noted in the pen-and-pad session Democrats didn’t go after McConnell nearly as aggressively as the GOP did against Daschle, national Democrats were much more involved in McConnell’s race than in previous leaders’ elections.

In addition to the DSCC’s spending, Republicans point to a number of other instances, including comments by a Reid aide in a local news story late in the campaign that they say was a clear intrusion by the Democratic leader into the race.

Mollineau, however, denied Reid or his office was attempting to insert itself into the race and said it was simply an effort to respond to criticisms of Reid that had been leveled by McConnell in the closing days of the campaign.

“Our office has always responded when necessary to correct the record. That will continue over the next two years,” he said.

But Republicans also point to a teleconference Reid reportedly conducted in April with McConnell’s opponent, Bruce Lunsford (D). In the call with donors, Reid denounced Republican “obstructionists” and urged them to help fund Lunsford’s campaign.

These and other real or perceived slights have led many Republicans to believe Reid was deeply involved in the campaign against McConnell. Democrats made “no effort to hide who was helping pull the strings,” one Republican said, adding that the 2008 campaign “provided clarity on the ground rules for Nevada in 2010.”

Indeed, the political landscape in Nevada could face some major changes. For instance, while Reid and outgoing National Republican Senatorial Committee Chairman John Ensign (Nev.) have long had a non-aggression pact, Ensign warned Wednesday that Reid is vulnerable this cycle and Republicans should go on the attack.

Ensign also said that given the political dynamics of the state, Reid can expect a vigorous challenge.

The Nevada Republican recalled that when he ran against Reid in 1998, the Democrat’s disapproval rating never went higher than 38 percent. Today, he said, public polling shows Reid with significantly higher negative numbers. “If I was looking at that race, I would say that’s an attractive race to run,” he noted. But Ensign also acknowledged that much work needs to be done rebuilding the state GOP. “We have a lot of work to do in my state, and in all the Mountain states.”

Sen. John Cornyn (Texas), who is taking over the NRSC for the 2010 campaign, said that while it is “premature to say” Reid will be the top target of the cycle, he committed to aggressively finding a quality candidate to run against Reid and to boost the GOP’s fundraising efforts.

“We’re going to aggressively recruit and support candidates in every state where we think we have a chance,” Cornyn said.

Democrats and Republicans familiar with the dynamic said it is unclear how serious the rift between the two men may ultimately be, or whether an aggressive campaign against Reid will further erode relations. While Reid is known for often having a strong temper — and a difficulty in controlling his tongue — those who know Reid said he is focused on legislating and will look to keep politics out of the chamber as much as possible.

“Sen. Reid is focused on governing. We have an enormous opportunity over the next two years to pass meaningful legislation for the people of Nevada and the people of this country. And that’s where he’s focusing his energy,” one Democrat familiar with Reid said.

But one veteran Democrat warned that Reid is not afraid of a fight, saying the Majority Leader “ain’t afraid to whip out the old Searchlight sling blade and cut their nuts off.”