Sen. Dean Heller had barely taken the oath of office Monday when the political gamesmanship between himself and Majority Leader Harry Reid (D-Nev.) began.

The Nevada Republican disputed assertions from the Majority Leader’s camp that the two had agreed to a nonaggression pact, even as a senior Democratic Senate aide affirmed that the Nevada colleagues met privately last Thursday and reached an “understanding” to avoid personal, inflammatory attacks against each other during Heller’s 2012 Senate campaign.

The aide described the accord as similar to the agreement observed for nearly 12 years by Reid and John Ensign (R), who resigned from the Senate last week amid an ethics investigation.

Heller — appointed to replace Ensign by Gov. Brian Sandoval (R) — confirmed Thursday’s meeting with Reid, saying the two met at the Majority Leader’s invitation and had a cordial discussion about Nevada issues and how the Senate works. But Heller said unequivocally that the two did not agree to a nonaggression pact or any similar deal. However, he described Reid as gracious, said their relationship was comfortable and predicted they would agree on many local issues.

“That’s news to me. We did not have that particular discussion,” Heller told Roll Call when asked about the agreement. “If you’re asking if there’s a [nonaggression pact], that is not happening.”

However, the senior Democratic Senate aide stood by the contention that the Majority Leader and his newly installed GOP colleague had agreed to refrain from criticizing each other, either publicly or privately. It is the same understanding Reid has reached with every Republican he has served with since advancing to the Senate in 1987 — beginning with Paul Laxalt — the aide explained. Such an agreement, this aide said, allows for fundraising and campaigning but precludes nasty rhetoric.

Per Senate tradition, Reid walked Heller down the aisle at his swearing-in ceremony on the floor. The former 2nd district Congressman said the Majority Leader has been helpful in aiding his transition from the House and has been open with advice on how to succeed as a Senator. In a statement provided to Roll Call, Reid was complimentary of Heller.

“I welcome Dean Heller to the United States Senate,” he said. “As Dean transitions from representing a single district to the entire state, I look forward to working with him to make the tough choices that will help our state and our citizens recover.”

What appears clear is that this early spat has everything to do with Nevada politics and the 2012 Senate race.

Heller cannot win his win his state in 2012 — a presidential year — without the support of Democrats and independents. In fact, Heller acknowledged there was no “upside” to he and Reid lashing out at each other. He said his policy was to be respectful during disagreements with colleagues, but he made clear his opposition to any nonaggression pact and took pains to highlight his differences with Reid.

Despite signals from Reid that his political support for Heller’s Democratic opponent could be muted, there is ample reason to believe Reid will be an active behind-the-scenes player in the election. The Senate electoral map appears to favor the Republicans, and Reid’s bare four-seat majority hangs in the balance.

Democrats in Nevada and in Washington, D.C., said they expect the Majority Leader to fight hard to oust Heller and install a Democrat, presumably Rep. Shelley Berkley.

Democratic campaign operatives monitoring the Nevada race say that Reid has already been “extremely helpful” and that they expect him to work diligently behind the scenes to flip Heller’s seat. One Democratic strategist who has worked in the Silver State said Reid is cognizant that the race for Nevada Senate could determine whether he remains Majority Leader.

“There is no question that Shelley Berkley will have his full support,” the strategist said. “That being said, Sen. Reid is such a skilled politician that whoever ends up winning the race will believe that Sen. Reid did or did not do something important to bring about that outcome.”

The Berkley team is convinced that Reid is prepared to go to the mat to help her defeat Heller. Berkley has the support of the Democratic establishment, but she must first get through primary opponent Byron Georgiou, an attorney.

“Whatever he decides to do, he’s raised money for her and continues to have an integral role in what the state party does,” a source close to Berkley said. “The long arm of Harry Reid is definitely out there.”

Heller does not have a primary opponent, but that could change if the GOP base gets restless or is disappointed in their new Senator’s performance, or in his closeness to Reid.

Republican National Committeewoman Heidi Smith said the new Senator was wise not to agree to a pact.

The dynamics, she said, are different than with Reid and Ensign. Both Reid and Ensign are based in Las Vegas. But Reid is not as well-liked in the north, such as the Carson City area where Heller resides. That fact might not be lost on Reid and could be why he is pushing the narrative that he and Heller have agreed not to criticize each other.

“If Heller is smart — and I think he is — there will be no nonaggression pact. What good would it do him?” Smith said. “That Ensign nonaggression pact left most Republicans with a bad taste — it made him look weak and too close to Reid.”

Being seen as Reid’s friend is one way to hurt a Republican’s reputation, Smith added.