Wonder what caused them to backtrack? Blowback from legal experts who know what they're talking about maybe?

The president is essentially the ultimate arbiter of what is classified and what is not.

No, Trump did not break the law in talking classified details with the Russians

"Intelligence officials say President Trump might have damaged relations with allies, who will now be more cautious in sharing sensitive information with the United States. Democrats say he’s a hypocrite, having lambasted Hillary Clinton for her own handling of classified information. But when Trump spoke about highly classified information with Russian officials in a White House meeting last week, he did not break the law, legal analysts say.

The president is essentially the ultimate arbiter of what is classified and what is not. While the heads of particular agencies also have original classification authority — the power to deem material classified or not classified — their authority is limited to their departments and bound by their departments’ particular rules.

The president, as the head of the executive branch, knows no such restrictions — his power on the matter comes straight from the Constitution, legal analysts say. ....."

https://www.washingtonpost.com/world/national-security/no-trump-did-not-break-the-law-in-talking-classified-details-with-the-russians/2017/05/16/e9efd2cc-3a54-11e7-8854-21f359183e8c_story.html?utm_term=.965b05805b35