Even though he bashes anonymous sources, Trump uses them himself

— -- President Donald Trump used part of his speech at an annual gathering of conservatives today to take aim at reporters' use of anonymous sources, but failed to note that he uses unidentified sources himself.

"They shouldn't be allowed to use sources unless they use somebody's name," Trump said in his speech at the Conservative Political Action Conference.

The president didn't mention that his White House like every previous administration has officials serve as unnamed sources frequently as a way of informing reporters of policy and operational matters. The media also uses anonymous sources to protect the identity of people who might fear retribution for sharing sensitive information.

Hours before the president spoke at the conservative conference, for instance, the White House invited reporters to a "background briefing" where it was insisted upon that the media not reveal the names of officials holding the information session.

There are also examples from before, during and after Trump's presidential campaign when he made claims without attributing his sources.

His birther claims

Over several years, Trump used unidentified sources to claim that former President Obama was not born in the United States, which if true would have made him unqualified to be president.

For example, Trump tweeted in August 2012: "An 'extremely credible source' has called my office and told me that @BarackObama's birth certificate is a fraud."

Not until September 2016, after Trump became the Republican nominee for president, did he publicly acknowledge that Obama was born in the U.S.

Unsupported claims during the campaign

Another example of Trump's making a claim without specific sources came in November 2015, when he asserted that he saw "thousands" of people in the United States cheering the attacks on Sept. 11 that brought down the World Trade Center.

During an interview with ABC News' George Stephanopoulos, Trump said he "watched in Jersey City, New Jersey, where thousands and thousands of people were cheering as that building was coming down. Thousands of people were cheering."

At a campaign event the day after the interview, he doubled down on that assertion.

"Lo and behold I start getting phone calls in my office by the hundreds, that they were there and they saw this take place on the internet," Trump said in Ohio.

ABC News checked a variety of footage from the time of the attacks and the weeks after, finding no basis for his claim.

Months later in May 2016, Trump repeated an unverified report from The National Enquirer -- which based its story on anonymous sources -- that the father of one of his GOP primary opponents, Texas Sen. Ted Cruz, had been photographed with Lee Harvey Oswald before Oswald killed former President John F. Kennedy.

"I mean, what was he doing — what was he doing with Lee Harvey Oswald shortly before the death? Before the shooting?" Trump said during an interview with Fox News. "It's horrible."

The Cruz campaign immediately denied the claims made by The Enquirer and criticized Trump for his remarks.

ABC News' Jon Karl and Serena Marshall contributed to this report.