Donald Trump so far is just a presidential candidate. Yet along with his baying partisan hounds in Congress and his angry throngs of devoted followers, he has successfully bullied and intimidated the head of the FBI into discrediting himself and his institution and doing untold damage to the American political system. In case you wondered what life might be like under a Trump presidency, consider this a preview.

FBI Director James Comey is by all accounts a man of integrity and principle, including the principle of nonpartisanship. He made a determination in July, following a lengthy investigation, that Hillary Clinton should not be prosecuted.

No one had reason to believe that Comey, a Republican who has served in administrations of both parties, made his decision for partisan reasons. As he said, it was "not even close." Yet at the time of his decision, he did something extraordinary and contrary to normal prosecutorial standards: He explained his decision; he talked about the investigation; he even expressed his opinion of Clinton's behavior.

Why? There was no good reason except fear of the partisan backlash from Trump and the Republican Party. Comey might have told himself that the American people needed reassurance that his decision was fair and nonpartisan, but if so, he was foolish. Anyone who was reassured probably did not require an explanation -- they trusted the judicial system. It was the Trump supporters, and the Republican Party, who could not be reassured, no matter what Comey said.

Trump's entire campaign boiled down to one argument, summed up in his ever-elegant designation of his opponent as "Crooked Hillary." That was all he had. At his political rallies, even at the Republican National Convention, he encouraged his devoted throng to shout "Lock her up!"

While many Republicans no doubt believed she had to be guilty of something (with the same confidence that many Democrats believed George W. Bush lied the nation into war in Iraq), they also needed her to be found guilty. With a sure loser as their nominee, it was their only hope.

Republicans had become a lynch mob, demanding frontier justice, and they howled in outrage when Comey refused to participate in the hanging, accusing him of unfairly rigging the election when all he had done was his job.

A more courageous man would have kept silent and taken the heat. Comey, however, succumbed to the pressure. He did so in July, and he did so again last week, when he wrote his letter informing Congress that the FBI had come across new emails, even though he had no reason to believe there was anything incriminating in them and even though in so doing he violated Justice Department guidelines against taking such action so close to an election.

He was cowed by the mob, pure and simple.

The most worrying part of all this is that Comey's unwillingness to stand up to Trump and take the heat from Republicans may be a harbinger of worse things to come if Trump is elected.

There are very good reasons why the government makes no comment after it decides not to pursue criminal charges, why it offers no explanation and certainly expresses no opinions about the person who has been investigated. It is a dangerous abuse of the federal government's power.

Imagine that this happened to you. The government investigates and doesn't find sufficient grounds to prosecute, but releases selective bits of information it uncovered and publicly chastises you for bad, if noncriminal, behavior. Now imagine that the government did this to members of the opposition party or administration critics. No charges, just lengthy investigations, selective leaks, and public chastisement.

And, finally, imagine what would happen if the government were in the hands of someone who has no respect for democratic norms and practices, who loudly proclaimed as a candidate that he would investigate and lock up his opponent, would use the law to go after newspapers that criticized him, and would pursue legal action to quiet critics. We would be one step away from tyranny.

One might hope that all those conservative thinkers who have been warning against the federal government's allegedly tyrannical tendencies for so many years would find this troubling. But of course they won't, because they have succumbed to the same lynch-mob mentality that Comey caved to that now threatens the integrity of our electoral process.

Robert Kagan is a senior fellow at the Brookings Institution. He served in the State Department from 1984 to 1988.