It’s crunchtime for Donald J. Trump.

By Monday, March 25, the former president must secure an appeal bond for roughly half a billion dollars in his civil fraud case in New York, and his ability to do so was called into question this week.

In a court filing, Mr. Trump’s lawyers revealed that he had been unable to secure an appeal bond despite “diligent efforts” that included approaching about 30 bond companies.

While Mr. Trump this month managed to post a $91.6 million bond in his defamation case against the writer E. Jean Carroll, securing the deal at the 11th hour from a large insurance company, he lacks the assets needed to secure the far bigger guarantee for the fraud case.

If he cannot produce the bond in time, Mr. Trump faces the possibility of financial disaster and humiliation. New York’s attorney general, Letitia James, who brought the fraud case, would be entitled to collect the $454 million and could move to freeze some of Mr. Trump’s bank accounts.

She could also seek to seize some of his New York properties, and public records show that Ms. James has formally posted the judgment in Westchester County, a preliminary step needed to stake a claim to Mr. Trump’s private estate and golf club there. Yet any effort to seize property would most likely trigger a lengthy court fight with an uncertain result.

Mr. Trump’s money problems spread well beyond New York. As the presumptive Republican nominee for president, he is facing increased pressure to raise money to fund his campaign, lagging behind his opponent, President Biden, in fund-raising.