Judy Woodruff:

Good evening, and welcome to this PBS special, "The Mueller Report," from "Frontline" and the "PBS NewsHour."

I'm Judy Woodruff.

As we come on the air tonight, special counsel Robert Mueller's two-year investigation into Russian interference in the 2016 election has been completed and delivered to the attorney general of the United States, William Barr.

However, very little of the report itself has been made public, other than a letter from Barr to congressional leaders briefly summarizing its findings.

The letter says that the Mueller investigation concluded that, while the Russians tried to interfere in the election process to benefit then candidate Trump, there wasn't evidence that the president or his team conspired or coordinated with the Russians in this effort.

And on the question of whether the president obstructed justice during the Mueller investigation, the letter notes that the prosecutor didn't reach a decision on that matter. It says the Mueller report doesn't conclude that the president committed a crime. It also doesn't exonerate him.

Barr, however, said he concluded there was no obstruction.

Many members of Congress are now demanding to see the entire Mueller report. That will surely be debated vigorously in the days ahead.

But now seems an ideal moment to step back and examine what we know about how this investigation unfolded and to analyze its initial impact and the next steps to come.

Later in this special, I will talk to the president's attorney, Rudy Giuliani, and to some top legal minds, who will help us understand where this is headed.

But, first, our colleagues at "Frontline" have done extensive reporting about the Mueller investigation and the Trump team over the past year, until the report was delivered to the Department of Justice on Friday.