Donald Trump waves after speaking at a campaign press event at the Mar-A-Lago Club in Palm Beach, Fla., on March 1. (Jabin Botsford/The Washington Post)

Even as major Republican donors coalesced Wednesday around a last-ditch effort to halt Donald Trump's march toward the GOP presidential nomination, resignation was setting in among some onetime Trump critics.

"It is too late," Republican media strategist Alex Castellanos, who had unsuccessfully urged top GOP contributors to back an anti-Trump campaign earlier in the cycle, wrote in an email. "There is a fantasy effort to stop Trump, like a fantasy campaign to stop yesterday but it exists only as the denial stage of grief."

He went on:

"If our self-indulgent Republican party establishment had really wanted to prevent a takeover of the GOP, they should not have gorged on political power while they failed to do anything to prevent the decline of the country. Our leaders could have led. They could have done more than say 'no' to Democrats while offering no alternative.

"They should have stood up for the change Donald Trump is bringing now but they didn’t.

Now, Trump has earned the nomination. He won it, fair and square and we should respect that. Donald Trump whipped the establishment and it is too late for the limp GOP establishment to ask their mommy to step in and rewrite the rules because they were humiliated for their impotence.

If Trump is going to be our nominee, as I believe he is, it is our mission to support Trump and make him the best nominee and president possible."

Castellanos, who said he has no interest working for the real estate mogul's campaign, said the reality of Trump's momentum is setting in across the party.

"I think it will soon be clear that Republicans have hired Donald Trump to do the job their previous hires have failed to do: bring change to Washington and make America great again," he wrote.

As results showed Donald Trump leading in at least six states on Super Tuesday, Sens. Ted Cruz (R-Tex.) and Marco Rubio (R-Fla.) argued that nominating him would be bad for the Republican party. Here are key moments from their speeches following the March 1 races. (Sarah Parnass/The Washington Post)