Donald Trump almost certainly would not have won the Republican presidential nomination if changes set in motion by Theodore Roosevelt had not occurred, an expert on Roosevelt said Saturday in Glen Cove.

Speaking at the annual meeting of the Theodore Roosevelt Association, Geoffrey Cowan said the presidential primary system that Roosevelt championed made it possible for a candidate like Trump to circumvent the Republican Party elite and win by direct popular vote.

Roosevelt was running in 1912 to regain the presidency after disagreements with his hand-picked successor, William Howard Taft.

He initially opposed efforts by progressives within the GOP to institute a primary system to replace the longtime method in both the Republican and Democratic parties of letting party leaders and elites determine nominees, said Cowan, 74, a University of Southern California professor and author of the recently published “Let the People Rule: Theodore Roosevelt and the Birth of the Presidential Primary.”

But when Roosevelt realized the GOP elite would back Taft, and not him, “TR embraced primaries and popular democracy as his core beliefs,” Cowan said at the Glen Cove Mansion.

“His campaign theme became, ‘Let the People Rule,’ ” Cowan said.

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The former president, whose home on Sagamore Hill is a national landmark, won nine of that year’s 13 primaries, but party elites succeeded in blocking Roosevelt, who then unsuccessfully sought the presidency as a third-party candidate.

“In the argot of today’s world, Roosevelt claimed that the process was rigged,” Cowan said.

For more than a half-century afterward, the primary system Roosevelt helped create was countered by the continued power of party leaders.

In 1968, Cowan helped organize a commission that reformed the Democratic primary system after the uproar when Hubert Humphrey won the Democratic nomination despite not winning a single primary. Cowan had backed anti-war liberal Eugene McCarthy.

The reformed system — in which the popular vote determines nominees — is in place in both parties today, although a 1984 change in the Democratic Party gave some sway to party elites who are called “superdelegates.” Some in the GOP are certain to push for Republican superdelegates if Trump loses on Nov. 8, Cowan said.

This year, Jeb Bush had the support of many GOP leaders, who differed with Trump on key issues such as trade and were suspicious of someone who had previously been a registered Democrat, the author said.

A historian writing a January Washington Post review of Cowan’s book said that “if Donald Trump wins the Republican nomination for president over the strenuous efforts of party elites to derail him, he ought to send a note of thanks to Geoffrey Cowan.”

This year is only the second time since the 1970s that the annual meeting of the Theodore Roosevelt Association has been held at or near Sagamore Hill National Historic Site, said Tweed Roosevelt, the association’s CEO and a great-grandson of the former president. A fundraising dinner was scheduled for Saturday night at Sagamore Hill. National Park Service Director Jonathan Jarvis was scheduled to speak.