WASHINGTON • A wave of prominent Republicans have announced their intention to skip the party's national convention in Cleveland this summer, the latest sign that Mr Donald Trump, who last week secured the number of delegates needed to clinch the Republican presidential nomination, continues to struggle in his effort to unite the party behind his candidacy.

The list of those who have sent regrets includes governors and senators - almost all facing tough re-election fights this year - and lifelong party devotees who have attended every convention for decades. Some are renouncing their seats like conscientious objectors.

"I could not in good conscience attend a coronation and celebration of Donald Trump," wrote an Indiana delegate, Mr Josh Claybourn, in a blog post as he resigned from his position.

The coolness towards Mr Trump amounts to a remarkable rebuke. A broad range of party leaders are openly rejecting the man who might be their nominee.

And the July 18-21 convention, usually a moment of public catharsis for political parties after contentious primaries, is shaping up to be another reminder of the disarray and disunity that is still rocking the Republican Party after a bitter 17-way fight for the nomination.

Even the two highest-ranking Republicans in the convention's host state of Ohio - Governor John Kasich and Senator Rob Portman, who is fighting to hold on to his seat - say they do not know if they will set foot in the convention hall.

Mr Kasich, who only four weeks ago quit the presidential campaign and has not endorsed Mr Trump, has no idea "what role if any he will have", a spokesman said. Several others of Mr Trump's former rivals for the nomination have said they will not attend or have not committed. Mr Jeb Bush, the former governor of Florida, will not be there.

Neither will Senator Lindsey Graham of South Carolina. "I'm sure it will be fun; I'm sure it will be entertaining," he said last week. "And I can watch it on TV."

Senator Rand Paul of Kentucky, who is a delegate as well as a former presidential candidate, has yet to decide. "TBD," a spokesman said. "The schedule is still being firmed up."

At least two former competitors of Mr Trump's are expected to attend: Governor Chris Christie of New Jersey and Senator Marco Rubio of Florida, who last week offered his services as a speaker should they be wanted.

Among those staying away are major corporations such as Coca-Cola, Microsoft and Hewlett- Packard. Just about every Republican senator in a difficult race is staying away, fearful of what the association with Mr Trump might do to reputations back home.

Scheduling conflicts seem to be a surprisingly common excuse for missing an event that was announced a year and a half ago.

Others offered mushy non-commitments. "Just as they're firming up the schedule, it kind of looks like there's a lot of stuff for me to do," said Senator Ron Johnson of Wisconsin, explaining why he probably couldn't make it.

Asked if Mr Trump had anything to do with his reluctance, Mr Johnson, who is in a heated re-election campaign, broke into a big smile and said: "Oh, of course not."

Four of the five living former Republican nominees are skipping the convention. Senator John McCain of Arizona is one of them. "I'm in a very tough re-election campaign," he said last week, explaining his expected absence.

"I don't even want to be involved," said Governor Larry Hogan of Maryland in an interview in March. "It's a mess. I hate the whole thing."

NEW YORK TIMES