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The FBI has raided the office, home and hotel room of Michael Cohen, Donald Trump's long-time personal lawyer, business adviser and fixer-of-uncomfortable-problems. Now Mr Cohen himself has become the uncomfortable problem, with no easy fix in sight.

There's basically no precedent for this sort of action in modern US presidential politics. And Mr Trump's response on Monday afternoon - an unprompted, extended tirade that used the word "disgrace" or "disgraceful" nine times - hints that the president is concerned… and angry.

Here are a few reasons why the Cohen raid is a significant development in the ongoing presidential investigations - and a growing headache for the White House.

The man under the microscope

Fifty-one-year-old New Yorker Michael Cohen has a law degree, but his past duties for Mr Trump were not typical attorney obligations.

While he did provide counsel, he also was one of the Trump Organization's lead negotiators on foreign business dealings, the man who would send threatening legal letters to Trump critics and - at least in the Stormy Daniels episode - someone who would arrange to keep potentially embarrassing information about Mr Trump under wraps.

"They say I'm Mr Trump's pitbull, that I'm his right-hand man," Mr Cohen said in 2011. "What I am is a loyal employee. I like the man a lot."

In other words, Mr Cohen - although he severed his ties with the Trump business organisation in 2017 - has been deeply embedded in the Trump world for roughly a decade.

If he is under legal scrutiny, it could open a vast window into the inner workings of the president's business empire. His real estate dealings in Russia had already attracted the attention of special counsel Robert Mueller's team, and he was featured prominently in the now-notorious Christopher Steele dossier.

Even if the search leads nowhere, federal agents scrutinising a presidential lawyer's business is still a remarkable development. At the moment, however, there's no telling what law enforcement's efforts on Monday could turn up.

A second investigation

The issue isn't just what happened - federal investigators reportedly collecting documents and related information about Mr Cohen's tax records, business dealings and six-figure payment to secure the silence of Daniels, an adult film star who says she had an affair with Mr Trump. It's also who is doing the investigating.

According to media reports, the search was the result of information originally discovered by Mueller's investigation, but his office wasn't involved in the search. Instead, Deputy Attorney General Rod Rosenstein instructed the Mueller team to refer the matter to the US attorney for the Southern District of New York, which requested and executed the warrant.

Media playback is unsupported on your device Media caption Stormy Daniels: 'I was threatened'

Geoffrey Berman has served as the acting US attorney for the Southern District for more than a year, after Mr Trump fired his predecessor, Preet Bharara. He's a long-time Republican donor, including to Mr Trump's presidential campaign, and has reportedly recused himself from the investigation.

Because this is being handled by his office and not the special counsel, however, any move Mr Trump makes against Mr Mueller will have no impact on this inquiry, which appears to be focused on whether the payment to Daniels - and perhaps other women who have alleged romantic involvement with Mr Trump - violated tax, banking or campaign finance laws.

Mr Cohen says he made a $130,000 payment to Daniels in October 2016 out of his own funds in exchange for her silence. If that turns out not to be the case, or if the payment is considered to be the equivalent of campaign contribution, it could run afoul of federal disclosure rules.

Democratic presidential candidate John Edwards faced criminal prosecution in 2011 for undisclosed campaign payments he made to a former mistress.

In other words, this is not an academic consideration.

Privilege threatened

The FBI-conducted raid of Mr Cohen's property isn't a garden-variety search, either. Because Mr Cohen is the president's personal attorney, federal investigators had to comply with extra safeguards to avoid infringing on a client's right to confidential legal counsel.

Top-level Justice Department officials had to approve of the move, and extra personnel were involved in the process to ensure that "privileged" communications between Mr Cohen and his clients, including Mr Trump, were not disclosed to the investigatory team.

The sensitivity of the search was probably on the president's mind on Tuesday morning when he tweeted, "Attorney-client privilege is dead!"

Media playback is unsupported on your device Media caption Schumer to Trump: Attorney raid not an attack on US

The lawyer protections aren't iron-clad, however. There are exceptions to the rules, such as in cases where the lawyer is discussing topics outside the realm of agreed legal representation or the parties are involved in committing or concealing criminal activity.

If investigators conclude there is reason to believe that Mr Cohen's payment to Daniels violated banking, tax or campaign finance laws - and is able to convince a judge to concur - then material related to that act, even if it includes otherwise protected communications, could be admissible in court.

A storm is brewing

During a meeting with his military advisers on Monday the president embarked on extended remarks about what he viewed as the impropriety of the Cohen search.

He called his lawyer a "good man" and claimed that law enforcement "broke into" his office. Mr Cohen told CNN that FBI agents "were extremely professional, courteous and respectful".

Mr Trump reiterated that the investigations - including, presumably, the one involving Mr Cohen - were a "witch hunt". He again questioned the impartiality of those investigating him, asserted that there was no evidence of "collusion" between his campaign and Russia, and said Democrats should be the focus of scrutiny.

He called the investigation an "attack on our country" and "on what we all stand for" and entertained the possibility of firing Mr Mueller, as "many people" are saying he should do.

"So we'll see what happens," the president said.

Media playback is unsupported on your device Media caption Trump: FBI raid of my lawyer's office is "a whole new level of unfairness"

The most significant development out of the Cohen raid, then, is what it could set in motion.

The president relied on many of his worn phrases - "many people are saying" and "we'll see" - that have, in the past, hinted at future action. He has reportedly considered firing Mr Mueller in the past. Would the special counsel's role in all this be enough to push the president over the top?

Mr Trump again took swipes at his own attorney general and Deputy Attorney General Rod Rosenstein - himself a past target of presidential ire - who approved the New York office's raid. Could their positions be in jeopardy?

In a Russia investigation that has moved by increments over the past few months, the Cohen search represents a stunning development. There's a new front in the political and legal warfare, and a new series of exposures for the president and those closest to him.

Even if the president decides to act, however, the scope of the inquiry - and the potential damage that could result - just became much more challenging to contain.

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