Donald Trump's "running war" on the media is continuing into his presidency, with statements over the weekend calling into question the extent to which information from the White House can be trusted.

White House press secretary Sean Spicer on Monday will hold his first daily press briefing, at which he could face questions about a statement Saturday night that included demonstrably false assertions about the crowd size at Trump's inauguration and a promise by the new administration that "we're going to hold the press accountable."

Some Trump supporters will no doubt cheer the continued antagonism toward the media that was central to the Republican's campaign for president. Now the stakes are higher.

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White House Press Secretary Sean Spicer attacked media reporting of the size of the crowd at Friday's inauguration, claiming it was the largest ever. That's in contrast to reports that the size of Donald Trump's inauguration crowd was notably smaller than Barack Obama's.

Press secretaries have been lied to by their bosses, or misled reporters through the omission of information, but veteran journalist Dan Rather said Sunday it was the first time he could recall false material being delivered in this way.

"I hope that people will stop, pull back for what we in television call a wide shot and see what is happening," Rather said. "This is a deliberate propaganda campaign."

Spicer, a long-time Republican operative who most recently was the spokesman for the Republican National Committee and also worked for President George W. Bush, is known for fighting tenaciously for his employers. His briefing on Saturday followed a Trump appearance at the CIA where the president criticized the media for reporting his criticisms of the intelligence community. He also took exception to stories saying the crowd for Friday's inauguration was smaller than those for predecessor Barack Obama. Trump declared that journalists are "the most dishonest human beings on Earth," saying "I have a running war with the media."

Spicer made two unprovable statements in his briefing: that photographs of the audience at Trump's inaugural were intentionally framed to minimize the appearance of support, and that Trump drew the largest audience ever to witness an inauguration.

But he also made statements that were quickly disproven: that the Washington Metro system recorded more riders on the day of Trump's inaugural than when Obama was sworn in for his second term, that Friday was the first time that white floor covering was used on the Washington Mall, amplifying empty spaces, and that it was the first time spectators were required to pass through magnetometers to enter the Mall.

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Spicer's briefing, during which he did not take questions from reporters, was televised live on Fox News Channel and MSNBC. CNN did not air the session but showed highlights later.

Trump's first press conference after he was elected, held on Jan. 11, also took aim at the media. Coming hours after news reports revealed intelligence officials had presented Trump with unsubstantiated and salacious allegations regarding his relationship to Russia, Trump and his team condemned news organizations that disclosed details, calling out CNN and BuzzFeed as "disgraceful" and refusing to take questions from a CNN reporter.

Confronted by "Meet the Press" host Chuck Todd on Sunday with "falsehoods" stated by Spicer, Trump adviser Kellyanne Conway called them "alternative facts." She accused Todd of laughing at her and said he symbolizes how Trump has been treated by the media.

One person who has been in Spicer's position, former White House press secretary Ari Fleischer, said it seemed clear to him that Spicer was acting on orders from his boss. Press secretaries have to walk a fine line between reflecting the thinking and wishes of the president while trying to help the people covering him do their jobs, said Fleischer, who, like Spicer, worked for George W. Bush.

Fleischer said he never knowingly delivered false information to the press while at the White House.

"You can't do that," he said. "It will shorten your career."

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When Spicer faces the press on Monday, he needs to elaborate on his argument, "take the hard questions and demonstrate reasonableness," Fleischer said.

The conservative website breitbart.com led its site with an article headlined: "White House press secretary Sean Spicer blasts media's 'deliberately false reporting."' The article said that Spicer's "criticism of the media's fake news reporting resulted in a media meltdown on social media."

It's a crucial time for Spicer's reputation. A press secretary whose word can't be trusted has no value to anyone, said Terence Hunt, a long-time White House correspondent and editor for The Associated Press who recently retired.

"You can't tell lies in the White House," Hunt said. "Somebody will smoke you out, on issues large and small. The president's integrity and credibility are at stake in everything you say, so be super careful."

If the White House can't be trusted to tell the truth on a relatively trivial matter like crowd size, the public will wonder about the reliability of information on important topics like terrorism or the nuclear capabilities of North Korea, said Ben Mullin, a managing editor at the Poynter Institute who does a podcast on the relationship between Trump and the press.

Rather, a former CBS anchor who famously tangled with the Nixon White House during the Watergate era, said the situation saddened him.

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"I don't think the American people as a whole, whether they supported Donald Trump or not, want a situation where the press secretary to the president comes out and knowingly tells a lie," he said.