Donald Trump is on track to hand the Republican establishment an unprecedented defeat at the national convention in July, despite being outspent 3-1 by party leaders and their associates in their all-out effort to turn primary and caucus voters against him, according to a state-by-state delegate allocation analysis by The Washington Times.

By the time California and three other states count their votes from the last four primaries June 7, the brash billionaire businessman and TV star will be 74 or so delegates short of the 1,237 majority needed for the nomination, the analysis shows.

With so large a plurality in the offing, it is increasingly unlikely that the Republican establishment, fronted by 2012 presidential nominee Mitt Romney, will carry through with plans to change the convention rules to wrest the nomination from Mr. Trump and hand it to an establishment-approved candidate such as Marco Rubio or John Kasich, or even a noncandidate like House Speaker Paul D. Ryan, who is expected to be named the convention’s chairman and has the adoration of the party’s power brokers.

“I cannot imagine him not getting a majority on the first ballot if he’s only 74 delegates short of a majority,” said Republican superlawyer and Constitution scholar James Bopp Jr.

“Even if he were 174 short, if he had a substantial lead in delegates, it would likely be politically unacceptable for the anti-Trump forces to deny him nomination,” said Mr. Bopp, also a former Republican National Committee vice chairman.