Michael Cohen outside the federal courthouse in Manhattan on Thursday. (Julie Jacobson/AP)

It was a dizzying week for special counsel Robert S. Mueller III’s investigation. The election is over, and after more than a year of haggling, Mueller finally received written answers from President Trump — not as good as testimony or a live interview, but better than nothing. With these milestones behind him, it feels as though Mueller is rapidly moving toward a resolution of his ultimate questions : What were the Trump campaign’s ties to Russia, and were any of them criminal?

The latest development was Thursday’s guilty plea by Michael Cohen, the president’s former personal lawyer, who admitted to lying to Congress about Trump’s efforts to develop a 100-story tower in Moscow. Negotiations over the project took place during the spring of 2016, just when Trump was locking up the Republican nomination. But Cohen had told Congress the deal was abandoned in January, before the Iowa caucuses.

Cohen was the latest in a string of Trump campaign officials — including former national security adviser Michael Flynn and former adviser George Papadopoulos — to plead guilty to lying about their contacts with Russians. When prosecutors see people lying to investigators, the obvious question is: What are they trying to hide? As Mueller’s inquiry enters the final stages and prepares to answer that question, there are two main possibilities.

The first is that Trump officials conspired with Russians in illegal efforts to affect the 2016 election and then lied to conceal their Russian ties. This would be the grand conspiracy, or “collusion,” that has always been the central question in Mueller’s investigation. It would mean, for example, charges that members of the campaign knowingly collaborated with foreign agents in an effort to damage Hillary Clinton by illegally deploying stolen Democratic emails during the fall of 2016. Mueller’s apparent recent focus on possible connections between WikiLeaks, Julian Assange and Trump cohorts such as Roger Stone seems directed toward investigating whether there was any such conspiracy.

But executing a complex criminal conspiracy with foreign accomplices would require a level of sophistication and ability that was not generally on display in the Trump campaign. It remains to be seen, but the campaign’s documented contacts with Russians may prove to have been naive, bumbling, reckless, sleazy, unpatriotic or some combination thereof — but not criminal.

Which leads us to the second possibility: The president and his associates have lied about contacts with Russia not because they were illegal but because they would have been politically disastrous. After all, standing alone, it’s not illegal for Trump to pursue a branding deal involving a tower in Russia, even while running for president. It’s not even necessarily illegal to meet at Trump Tower with Russians who promise compromising information about your opponent (depending on what, if anything, was agreed upon or done as a result of the meeting). The president himself has repeatedly and emphatically denied any connections to Russia but, even if some of those statements are untrue, lying to the public or the press is not illegal. If politicians could be jailed for that, we might as well just erect bars around the Capitol building and call it a day.

But news that, during the Republican primaries, Trump was actively pursuing business negotiations with our global adversary would have been political dynamite. Reports of events such as the Trump Tower meeting would have contradicted Trump’s claim that he had no Russian ties and fueled concerns that Moscow might have some leverage over the president. And any suggestion of possible complicity with Russians threatened to undermine the legitimacy of his election — one thing that Trump clearly cannot tolerate.

During his guilty plea, Cohen said he lied to Congress about the Moscow real estate deal to be consistent with Trump’s “political messaging.” Others already charged or yet to be charged may have lied for the same reason: not to conceal other criminal conduct, but to shield the president and his administration from the political consequences of the truth.

If it’s primarily about the coverup, then one question becomes who else was involved. Did the president or other administration officials direct Cohen or others to lie? The president’s tweets themselves may not be criminal, but anyone who encouraged or instructed others to lie could be implicated in a coverup conspiracy.

The other question becomes the political consequences. Mueller is expected to write a report detailing what he has found. Business and campaign ties to Russia that were concealed from the public may fall short of criminal conduct but still yield politically disastrous results for Trump.

But as far as criminal charges are concerned, Mueller’s investigation may well end not with charges of an international conspiracy but, instead, with a number of Trump associates convicted on charges of lying about Russia for political reasons. It’s common for defendants to be convicted for covering up conduct that was not necessarily illegal — just ask Martha Stewart or the freshly pardoned Lewis “Scooter” Libby.

In Washington, of all places, people should know that, sometimes, it’s the coverup that gets you.