Miami-based US District Judge Darrin Gayles said Trump did not meet the "actual malice" standard that public figures must clear in defamation.
That means they must prove not only that a public statement about them was false but also that the media outlet or person who made the statement knew or should have known that it was false.
"This complaint comes nowhere close to this standard," Gayles wrote.
"Quite the opposite."
The judge wrote that the WSJ's reporters reached out to Trump for comment beforehand, and printed his denial.
That allowed readers to decide for themselves what to conclude, cutting against Trump's assertion that the newspaper acted with actual malice, the judge said.
Gayles said Trump could file an amended version of the lawsuit by April 27.
In his lawsuit against the WSJ and Rupert Murdoch, Trump called the alleged birthday greeting "fake" and sought $US10 billion ($A14 billion) for what he called damage to his reputation.
News Corp's Dow Jones, the WSJ's parent, defended the accuracy of its July 17, 2025, article.
