Conservative donor Rebekah Mercer attends the Media Research Center's 2015 annual gala in Washington. (Courtesy of Media Research Center)

Amid the tensions that lingered between Sen. Ted Cruz (R-Tex.) and GOP presidential nominee Donald Trump after their heated primary fight, there has been one key bridge between the two men: their relationship with the Mercers, the wealthy conservative benefactors who have poured millions into boosting both their political fortunes.

Cruz's long-coming endorsement of Trump on Friday was widely interpreted as a sign of the family's influence in both camps. After giving $13.5 million to a super PAC that backed Cruz in the primaries, billionaire hedge fund executive Robert Mercer and his middle daughter, Rebekah, remade the group into an anti-Hillary Clinton vehicle and urged other conservatives to rally around Trump. They even publicly castigated Cruz after he declined to endorse his former rival at the Republican convention.

In recent weeks, the Mercers played a role behind the scenes encouraging a detente — efforts that carried weight because the family is highly regarded by both camps, according to a person familiar with the situation.

Another person who is close to the Mercers declined to detail the role they played, but said: "This election could not be more stark. They encourage everyone they know to vote for Donald J. Trump."

And in a statement released to The Washington Post, Robert and Rebekah Mercer made it clear that they approved of Cruz's decision.

"For the first time in many decades, American voters have the chance to turn their backs on the political elite, an elite both Democrat and Republican, that has chosen as its leader Hillary Clinton, a dedicated foe of both the First and Second Amendments and the most dishonest, corrupt, and incompetent politician ever to seek the American presidency," the statement read. "Even such great Americans as Mitt Romney and George Bush have stooped to endorse Mrs. Clinton rather than risk electing a president who follows the will of the people. We have long supported Senator Ted Cruz.  He has waged a fearless battle against the elite throughout his career.  We are delighted that he is joining us and a growing army of Americans in support of Donald J. Trump's candidacy for the presidency of the United States of America."

(Neither Romney nor either of the Bush presidents — George H.W. Bush and George W. Bush — has endorsed Clinton. A family friend said George H.W. Bush plans to vote for Clinton, but his aides have not publicly confirmed that.)

The statement suggests that Cruz once again has an ally in the Mercers, who chided him in July in a statement to the New York Times. "We need ‘all hands on deck’ to ensure that Mr. Trump prevails," they said at the time, adding: "Unfortunately, Senator Cruz has chosen to remain in his bunk below, a decision both regrettable and revealing.”

It also underscores the family's rising influence as a major player in Trump's orbit. Key to that has been Rebekah Mercer, a 42-year-old former Wall Street trader who has taken the lead in guiding the family's political investments. Shortly after Cruz dropped out of the primary, she and Ivanka Trump bonded over a lunch at Trump Tower. Among the top officials running the Trump campaign are a trio of operatives close to the family, including campaign manager Kellyanne Conway, a Mercer friend who had been helming their super PAC.

Robert Costa contributed to this report.