It's a cliche in the legal world: A prosecutor could persuade a grand jury to indict a ham sandwich. That is because the standards for bringing charges are relatively low — "probable cause" that a crime has been committed, as opposed to the "beyond a reasonable doubt" hurdle that comes before a defendant is convicted in a trial.
In addition, usually only the district attorney or the state attorney (or whatever they call the prosecutor) can offer evidence to the citizen grand jurors. Defense lawyers are almost never allowed to refute the allegations or to provide any explanation.
The point is, prosecutors have a ton of power, and special counsels are super-duper prosecutors. Robert Mueller is one of those, and now he's made his first ham sandwiches. They are big ones: Paul Manafort, a former Donald Trump campaign manager, along with Manafort aide Rick Gates. Their 12-count indictment includes serious felony charges: money laundering, tax evasion, failure to register as a foreign agent and conspiracy against the United States while working on behalf of Ukrainians with close ties to Moscow. Former Trump campaign adviser George Papadopoulos also pleaded guilty to one count of lying to the FBI about his Russian contacts. Yes, it's a crime to lie to FBI agents, which only enhances the government's power in criminal matters.
Ultimately, the guy who was not indicted today is a certain president of the United States. Mueller was appointed to determine whether there was criminal collusion with Vladimir Putin's agents by Donald Trump or his campaign underlings to swing the election Trump's way. Mueller's mandate, as is the case with all independent counsels, extends to any crimes that are uncovered during the investigation. Hence these formal accusations against Paul Manafort and Rick Gates.
As big a deal as the charges are and as serious as the allegations they face are, Manafort, Gates and Papadopoulos are not just ham sandwiches but potatoes, relatively small potatoes. Mueller must ultimately determine whether to charge Donald Trump. So he'll be putting the squeeze on those lower in this food chain to see whether any of the three will spill their guts about higher-ups to provide information about collusion that could bring down the president.
As for the president, he's doing what he always does when he's agitated: He turns to Twitter. Pointing out that these indictments weren't about collusion, he cleverly tweeted, "NO COLLUSION." That was after he pecked: "Sorry, but this is years ago, before Paul Manafort was part of the Trump campaign. But why aren't Crooked Hillary & the Dems the focus?????"
First of all, Hillary Clinton is off the point. As Trump reminds us every chance he gets, he beat her. Her misdeeds, if any, would not result in her impeachment. But that's getting way ahead of what has happened so far. Even if Mueller ultimately charges Trump with any crimes, as president of the United States, Donald Trump first would have to be removed from office before facing legal consequences. That could be iffy even in extreme circumstances given how the Republicans in Congress are so terrified of his, uh, ham-handed politics.