From Cato Institute: Julian Sanchez:
On Monday, the Washington Post dropped a bombshell, reporting that Donald Trump had shared highly classified “codeword” intelligence—provided by an ally on the condition that it not be more widely disseminated—with Russian officials during their meeting last week. While administration officials initially issued fierce denials, national security advisor H.R. McMaster, who had himself blasted the story as “false” in a carefully-worded statement, effectively confirmed the key elements of the report at a press briefing Tuesday morning. While McMaster repeatedly insisted that Trump’s decision to share information had been “wholly appropriate,” his remarks (perhaps inadvertently) raised several additional grounds for concern.
First, let’s dispense with the obvious: Classification authority in the United States flows from the president, and so a president is legally entitled to declassify or disclose information as he sees fit, for any reason or no reason at all. This is a case where that infamous Nixonism—”When the president does it, that means it is not illegal”—actually applies. Nobody, as far as I can tell, is seriously disputing that. It’s also true that presidents often choose, for strategic or diplomatic reasons, to share particular pieces of intelligence with foreign governments. Yet this does not appear to have been a “routine” instance of such sharing, as McMaster sought to characterize it—not by a longshot.