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Sen. Mike Lee has had a somewhat strained relationship with his Republican colleagues, and yet seven of them, including Sen. Orrin Hatch, have contributed to his 2016 re-election effort.

National Republican Senatorial Committee (NRSC) leaders also say they are fully behind him.

But Hatch isn't ready to make a firm commitment. Sure, his political action committee, OrrinPAC, has given Lee $10,000, but Utah's long-serving senator says money doesn't equal an endorsement.

"I'm just helping a colleague," Hatch said Wednesday. "I don't think it's time to start endorsements, to be honest with you. It's a little premature. We're a year and a half away from those elections, but [Lee's] doing fine."

At this point, Lee has no announced challengers, having ducked potential bids from the likes of Josh Romney, the son of former presidential candidate Mitt Romney, and Thomas Wright, the former chairman of the Utah Republican Party, among others. On the Democratic side, the top potential challengers, former Rep. Jim Matheson and Salt Lake County Mayor Ben McAdams, are also taking a pass.

And yet, Hatch has decided to sit back and wait. This isn't how he operated when Bob Bennett, R-Utah, was in the Senate for three terms. When Bennett was up for re-election, Hatch immediately backed his friend and Bennett did the same for Hatch. Lee defeated Bennett in the 2010 Republican convention and went on to claim the seat as a tea-party Republican, often at odds with party leaders and most colleagues.

Lee refused to endorse Hatch in 2012 until he won the Republican nomination by defeating Dan Liljenquist in a primary. Lee said it would be inappropriate for a man who defeated an incumbent to endorse in a primary.

Hatch won the nomination and secured his seventh, and what he says is his final, term in office. And now, he's the one withholding his endorsement.

Lee's team isn't concerned.

"Senator Hatch is right in terms of it being early. We are certainly not out there pounding people's doors for endorsements," said Boyd Matheson, Lee's chief campaign strategist. "We are grateful for the support Senator Hatch has provided. He co-hosted an event at the NRSC for the boss."

That fundraiser, earlier this spring, helped Lee ramp up his campaign contributions, which were anemic in his first years in office. But in the past three months, he raised a robust $759,200 and now has $1.2 million in available cash.

The NRSC is an organization comprised of Republican senators meant to support incumbents, and Hatch has been a chief fundraiser for them in recent years. Ward Baker, NRSC executive director, said his group is "100 percent behind Senator Lee and will work day and night to ensure he can continue to serve Utah families."

So far Lee has received contributions from seven of the 54 sitting Republicans, including contributions from Sens. Mike Enzi, R-Wyo., Cory Gardner, R-Colo., and Rob Portman, R-Ohio. And Boyd Matheson said Lee has participated in NRSC fundraising efforts.

But Lee has a far more complicated relationship with the caucus than Hatch does. His strategy to combat President Barack Obama's health reform led to a partial government shutdown and angry closed-door meetings with his colleagues. Most recently, Lee missed a key vote on trade authority that irritated Hatch's camp and senior GOP leaders.

While Hatch and Lee are congenial, they have had frequent disagreements, including on issues such as immigration reform.

Many expected Lee to face a strong challenge from within his party as he seeks a second term.

That hasn't happened so far, even as Josh Romney and Spencer Zwick, a key fundraising adviser to Mitt Romney, tried to find a candidate to support. No one has stepped forward.

In the meantime, Lee has won the endorsements of former Utah Gov. Jon Huntsman and Zions Bank CEO Scott Anderson.

Thomas Burr contributed to this article.