Last year, the White House was warned by U.S. intelligence agencies that Rudy Giuliani, President Trump's personal lawyer, was the target of a Russian intelligence operation, four former officials with knowledge of the matter told The Washington Post.

The goal of the operation was to feed misinformation to Trump, intelligence officials said, and National Security Adviser Robert O'Brien took the warnings to heart, letting Trump know during a private conversation that any information Giuliani brought back from his trip to Ukraine should be considered contaminated by Russia, the Post reports.

Giuliani went to Ukraine searching for information he hoped would discredit Democratic presidential nominee Joe Biden and his son, Hunter Biden. He was not the target of U.S. surveillance, but Giuliani did meet with suspected Russia assets, which is how intelligence agencies intercepted his communications and were able to warn the White House.

One former official told the Post that members of the intelligence community who knew about Giuliani's situation talked about "how hard it was going to be to try to get him to stop, to take seriously the idea that he was being used as a conduit for misinformation." They knew Russia meddled in the 2016 election and waged a disinformation campaign, and were concerned that Russia "may now be aided, unwittingly or otherwise, by individuals close to the president," the Post writes.

Trump, however, was undeterred; after O'Brien spoke with him about Giuliani, the president "shrugged his shoulders," one former official said, adding, "That's Rudy." Read more at The Washington Post.