Thomas Lifson's take on the situation (includes links and embedded video of McMaster's rebuttal/denial):
WaPo's latest 'Get Trump' article reveals Deep State methods to sabotage his presidencyhttp://www.americanthinker.com/blog/2017/05/wapos_latest_get_trump_article_reveals_deep_state_methods_to_sabotage_his_presidency.htmlExcerpts:
Once again, the mainstream media exploded yesterday with breathless tales of purported incompetence, or worse, treasonous betrayal of our deepest intelligence secrets to the Russians. Suddenly, the Kremlin has become the bad guy for Progressives, no longer worthy to hold the vast share of our uranium reserves it acquired under Hillary Clinton's supervision as secretary of state. And, as an article of faith, it was only because of the Russians that Hillary Clinton was denied her rightful term as president of the United States.
By now, you probably know the story that caused the newsroom at the Washington Post to erupt in celebration: "Trump revealed highly classified information to Russian foreign minister and ambassador."


[I bet you could count the non-progressives in that newsroom on
one zero hands.]
Based on anonymous sources (of course) said to be current and former officials (those former officials did not have official access, so they must be basing their opinions on hearsay – but never mind that basic flaw; this is a matter of getting dirt on Trump, so forget about standards), the story claimed that the president revealed the name of a town from which sensitive data on ISIS was received and thereby revealed too much about sources and methods used by an ally to provide us with intelligence.
There were only five U.S. officials at the meeting, and three of them have spoken publicly and denied that the Post's account is true. National security adviser (and former General) H.R. McMaster's words ought to be dispositive: "I was in the room. It didn't happen."