A prominent neoconservative figure and foreign policy commentator plans on headlining a fundraiser for Hillary Clinton Hillary Diane Rodham ClintonJeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Momentum growing among Republicans for Supreme Court vote before Election Day Warning signs flash for Lindsey Graham in South Carolina MORE’s presidential bid, according to a new report.

Robert Kagan, a former policy adviser for John McCain John Sidney McCainMomentum growing among Republicans for Supreme Court vote before Election Day McConnell urges GOP senators to 'keep your powder dry' on Supreme Court vacancy McSally says current Senate should vote on Trump nominee MORE’s White House run, will speak at the fundrasing event in Washington, D.C., next month, Foreign Policy reported Thursday.

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“[The] event will include an off-the-record conversation on America’s continued investment in NATO, key European allies and partners, and the EU,” an invite for the July 21 event said.

A ticket to the event on the rooftop of Washington’s Cambria hotel costs $100.

VIP tickets, including access to a reception with the event’s speakers and hosts, costs $250. Those paying $500 earn the title of “host” for the event in D.C.’s Logan Circle neighborhood.

Kagan is a senior fellow at the Brookings Institution and a co-founder of the Project for the New American Century.

Kagan’s appearance alongside Clinton is the latest sign Donald Trump Donald John TrumpUS reimposes UN sanctions on Iran amid increasing tensions Jeff Flake: Republicans 'should hold the same position' on SCOTUS vacancy as 2016 Trump supporters chant 'Fill that seat' at North Carolina rally MORE may be struggling with his appeal among conservatives.

The presumptive GOP nominee has struggled to win over some conservatives who are concerned with his lack of foreign policy experience. Brent Sowcroft, who served as an adviser to former presidents Gerald Ford and George H.W. Bush, and Richard Armitage, deputy secretary of State under ex-President George W. Bush, have said they'll back Clinton over Trump.

Kagan wrote a Washington Post op-ed last month disputing Trump’s credibility for holding the nation’s highest office.

“The Republican Party’s attempt to treat Donald Trump as a normal political candidate would be laughable were it not so perilous to the republic,” he wrote on May 18. “This is how fascism comes to America, not with jackboots and salutes (although there have been salutes, and a whiff of violence), but with a television huckster, a phony billionaire, a textbook egomaniac ‘tapping into’ popular resentments and insecurities, and with an entire national political party – out of ambition, or blind party loyalty, or simply out of fear – falling into line behind him.”

Clinton, the likely Democratic presidential nominee, leads Trump by 6 points nationwide.