Last week, Giuliani took to his Twitter account to decry special prosecutor Robert Mueller’s investigation into Russia’s interference in the 2016 election. In that tweet, Giuliani typed, “Mueller filed an indictment just as the President left for G-20.In July…” By failing to put a space between the period and the “In” in the next sentence, that section became a link. When people clicked on that link, they found a splash page that read (and continues to read), “Donald J. Trump is a traitor to our country.”

After discovering the gaffe, Giuliani tweeted on Tuesday that he didn’t mistype the tweet. Instead, he said that “Twitter allowed someone to invade my text with a disgusting anti-President message.” He said that he tested a period not followed by a space after he sent the original tweet out and no link was created.

“Don’t tell me they are not committed cardcarrying anti-Trumpers,” Giuliani said of Twitter.

Twitter denied Giuliani’s allegations. A spokesperson told Fortune that the company’s “service worked as designed.” The spokesperson added that whenever someone tweets a Web address, a clickable link is automatically created.

“Any suggestion that we artificially injected something into the user’s account is false,” the spokesperson said.

Twitter allowed someone to invade my text with a disgusting anti-President message. The same thing-period no space-occurred later and it didn’t happen. Don’t tell me they are not committed cardcarrying anti-Trumpers. Time Magazine also may fit that description. FAIRNESS PLEASE

— Rudy W. Giuliani (@RudyGiuliani) December 5, 2018

Still, that doesn’t directly answer Giuliani’s claim that he couldn’t recreate the issue a second time. Twitter’s service is intelligent enough to know when something is a domain and something is not. A period directly followed by “In” refers to domains that live on India’s top-level domain. It’s similar to .co.uk in the United Kingdom or .us in the United States. If, however, someone were to remove the space after a period and follow that with random letters or words that aren’t assigned to a top-level domain, Twitter won’t automatically convert that into a link.

In other words, if Giuliani tried again to post something with a .In, it would create a link. But he tried to post a tweet with .rudygiuliani, for instance, it wouldn’t create a link.

Giuliani has some history with technology. In 2017, he said that he would serve as Trump’s cybersecurity czar.