Former Florida Gov. Jeb Bush attacked President Barack Obama's approach to world affairs and took a veiled shot at Kentucky Sen. Rand Paul at donor conference hosted by casino billionaire Sheldon Adelson in Las Vegas Thursday night.

According to attendees at the closed-press function for $25,000-a-year donors to the Republican Jewish Coalition, Bush focused on economic policy in his remarks but also impressed the pro-Israel group with his defense of muscular American foreign policy.

"He showed a lot of knowledge about foreign policy that he must have been working hard to acquire," said Ari Fleischer, the former White House Press Secretary and a board member of the RJC, noting Bush discussed diplomatic challenges presented by countries like Ukraine, Russia and Moldova. "He was very rough on the president in terms of his handling of foreign policy, referring to the dangers of 'American passivity.'"

As buzz increases about a potential presidential bid, Bush spoke to about five-dozen top Republican Party donors at an event which has become a cattle call for the party's top leaders. In addition to Bush, New Jersey Gov. Chris Christie, Ohio Gov. John Kasich, and Wisconsin Gov. Scott Walker are among those addressing the RJC this weekend.

The son and brother of presidents, Bush cautioned the Republican party against "neo-isolationism," according to sources, a line universally understood as a shot at Paul. Bush also pushed back on Democratic attacks that whenever a Republican calls for a more activist foreign policy that they are "warmongering," Fleischer said. Fleisher's account was confirmed by two other attendees. "It was one of the strongest parts of his speech."

Bush, who was in office from 1999 to 2007, addressed the high-dollar donor dinner held at the mammoth private hangar owned by Adelson's Sands Corporation.

Bush devoted most of his address to immigration and education reform, attendees said."Governor Bush discussed the challenges facing our nation and the need to create high, sustained economic growth through policies that foster social and economic mobility," a spokesperson said.

Bush didn't reveal his thinking about 2016 when he was asked about his intentions, pivoting back to the policy challenges he believes face the country. According to a top donor close to Bush, while it could be quickly reactivated, his political operation remains "dormant."

Correction: An earlier version of this post said Bush had warned of "American pacificity." In fact he warned of the dangers of "American passivity."