Special Counsel Robert Mueller has impaneled a grand jury in Washington to investigate Russia’s interference in the 2016 elections, a sign that his inquiry is growing in intensity and entering a new phase, according to two people familiar with the matter.

The grand jury, which began its work in recent weeks, is a sign that Mr. Mueller’s inquiry is ramping up and that it will likely continue for months. Mr. Mueller is investigating Russia’s efforts to influence the 2016 election and whether President Donald Trump’s campaign or associates colluded with the Kremlin as part of that effort.

A spokesman for Mr. Mueller, Joshua Stueve, declined to comment. Moscow has denied seeking to influence the election, and Mr. Trump has vigorously disputed allegations of collusion. The president has called Mr. Mueller’s inquiry a “witch hunt.”

Ty Cobb, special counsel to the president, said he wasn’t aware that Mr. Mueller had started using a new grand jury. “Grand jury matters are typically secret,” Mr. Cobb said. “The White House favors anything that accelerates the conclusion of his work fairly.…The White House is committed to fully cooperating with Mr. Mueller.”

As many people know, there already has been a grand jury in Virginia, focusing on Michael Flynn.

Before Mr. Mueller was tapped in May to be special counsel, federal prosecutors had been using at least one other grand jury, located in Alexandria, Va., to assist in their criminal investigation of Michael Flynn, a former national security adviser. That probe, which has been taken over by Mr. Mueller’s team, focuses on Mr. Flynn’s work in the private sector on behalf of foreign interests.

So what’s the big deal with THIS new one in D.C?:

Grand juries are powerful investigative tools that allow prosecutors to subpoena documents, put witnesses under oath and seek indictments, if there is evidence of a crime. Legal experts said that the decision by Mr. Mueller to impanel a grand jury suggests he believes he will need to subpoena records and take testimony from witnesses.

A grand jury in Washington is also more convenient for Mr. Mueller and his 16 attorneys—they work just a few blocks from the U.S. federal courthouse where grand juries meet—than one that is 10 traffic-clogged miles away in Virginia.

“This is yet a further sign that there is a long-term, large-scale series of prosecutions being contemplated and being pursued by the special counsel,” said Stephen I. Vladeck, a law professor at the University of Texas. “If there was already a grand jury in Alexandria looking at Flynn, there would be no need to reinvent the wheel for the same guy. This suggests that the investigation is bigger and wider than Flynn, perhaps substantially so.”

It also suggests that Mueller is ready to move to the next phase of his investigation. It reflects that Mueller believes there’s a certain level of “there” there to justify a GJ investigation. You don’t talk to witnesses until you have a pretty good idea as to what the “truth” is (from wiretaps, etc.). That way, you can catch them in a lie.