President Donald Trump is reshaping the top tiers of US intelligence, replacing veteran operatives with his loyalists.

He is also is stepping up attacks on officials involved in the special counsel's Russia investigation.

Trump, emboldened since being acquitted in his impeachment trial, appears to have heeded advice from his allies to purge US intelligence agencies.

In comments Thursday, his chief of staff said "the deep state is 100% true" and officials who make Trump's life harder should be ousted.

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In the wake of his impeachment acquittal, President Donald Trump is intensifying his war against the US intelligence agencies he blames for the Russia investigation that cast a shadow over his presidency.

On Thursday, The New York Times reported that Trump angrily berated acting Director of National Intelligence Joseph Maguire last week after learning that one of Maguire's aides had briefed a bipartisan group of lawmakers that Russia was meddling in this year's presidential election in a bid to secure Trump's victory.

Trump this week replaced Maguire with Richard Grenell, the US ambassador to Germany who is considered a Trump loyalist.

He is said to be considering a congressional ally, Rep. Doug Collins of Georgia, to eventually nominate as full DNI, which requires congressional approval.

Another loyalist appointment followed Grenell's: On Thursday, Politico reported that Kash Patel, a National Security Council official who was hostile to the special counsel Robert Mueller's Russia investigation, had been promoted to advise Grenell.

The Daily Beast reported that two other top officials in the Office of the Director of National Intelligence were departing with Maguire, heightening the appearance of a full-scale purge.

Trump has long complained that a "deep state" of partisan unelected intelligence officials is conspiring to end his presidency.

He has alleged that not just Mueller's investigation but the impeachment investigation that ended with his acquittal in February are manifestations of the plot.

Trump has seized on attacks by senior former intelligence officials such as James Comey — the FBI director Trump sacked in 2017 for pushing ahead with the Russia investigation — and ex-CIA Director John Brennan as further evidence of the narrative.

Both men say they speak out against Trump because of what they consider his dangerous erosion of US norms.

Ric Grenell, the new acting director of national intelligence. Sean Gallup/Getty Images

A group of senior White House officials, including the former chief of staff John Kelly, had previously been seen as a moderating influence on Trump.

But with many senior administration officials having been replaced by loyalists, or by people in an "acting" capacity who can be easily removed, there is now little pushback.

The acting White House chief of staff, Mick Mulvaney, echoed the president's "deep state" rhetoric this week, telling students at Oxford University "the deep state is 100% true."

He argued that the role of government officials was not to defend the integrity of the institutions they worked for but to do the bidding of the president.

Unleashed by his impeachment acquittal, Trump has also renewed his attacks on officials behind the Russia investigation, encouraged by top allies who've urged him in media appearances to purge the US intelligence agencies they claim are hostile to his agenda.

Roger Stone was sentenced this week to over three years in prison. Drew Angerer / Staff / Getty Images

On Twitter this week, Trump has even floated the idea of suing Mueller.

The attacks have continued despite a report by the Department of Justice's inspector general last December that found no evidence of political bias in the genesis of the FBI's Russia investigation in 2016 (though it did highlight irregularities in securing surveillance warrants).

They gained added urgency this week with the sentencing of the former Trump adviser Roger Stone, who lied to Congress and threatened a witness while under investigation by Mueller.

Trump has attacked the judge in the case, Justice Amy Berman Jackson, and raged about the fact that officials involved in the Mueller investigation faced no prosecution. He says his allies found guilty of crimes were unfairly targeted.

Intelligence agencies are meant to be independent of partisan politics but have been particularly exposed to political pressure in the Trump era.

Critics say the president's attacks and counter-investigations are designed to have a chilling effect, deterring further scrutiny of the White House.

Former top intelligence officials, meanwhile, can only rage from the sidelines.

Brennan, the former CIA chief, warned that the US faced a crisis in the wake of Maguire's removal.

"We are now in a full-blown national security crisis," Brennan said.