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Mark Salter tweeted, "I'm with her" after Trump cited a National Enquirer story to slam Ted Cruz's father

Tuesday's tweet isn't the first time Salter has expressed a preference for Clinton over Trump

CNN  — 

Hillary Clinton has an unexpected ally: a former top adviser to John McCain.

Mark Salter, a confidant of the 2008 Republican presidential nominee, tweeted Tuesday “the GOP is going to nominate for President a guy who reads the National Enquirer and thinks it’s on the level. I’m with her.”

Salter was referring to a report Trump cited Tuesday morning from the tabloid, which alleged that it had identified Rafael Cruz, Ted Cruz’s father, in a photo with Lee Harvey Oswald months prior to the JFK assassination. CNN has not independently confirmed that report. “I’m with her” is a common phrase Clinton’s supporters have used in their social media posts to show their endorsement.

Tuesday’s tweet isn’t the first time Salter has expressed a preference for Clinton over Trump. In a February Real Clear Politics column, Salter lashed at Trump, writing, “he’s trying to make us the worst we can be to satisfy his own vainglory.”

RELATED: Donald Trump’s latest conspiracy theory involves Ted Cruz’s father

“If you can see him plainly and you love our country, you must vote against him. Even if that means electing Hillary Clinton,” Salter wrote.

Salter, a former chief of staff to McCain, served on both of the Arizona senator’s unsuccessful presidential campaigns as a senior adviser.

McCain, however, reiterated to MSNBC Tuesday night a statement he’s made before that he planned to support the GOP nominee, regardless of who it was, and said he would advise Trump on foreign policy if he asked him to.

“I would advise anyone who asks,” McCain said.

Also on Tuesday, South Carolina Sen. Lindsey Graham – a longtime friend of McCain’s – tweeted, “Any doubt left Trump is completely unhinged? His assertion Ted Cruz’s father was associated with Lee Harvey Oswald should remove ALL doubt.”

He added, “If we nominate Trump, we will get destroyed…….and we will deserve it.”

Salter and Graham’s tweets come as Trump appears close to securing the Republican nomination. A decisive win Tuesday in the Indiana primary would establish him as the all-but-certain presumptive Republican presidential nominee.