Trump's secrecy surrounding Putin "is not only unusual by historical standards, it is outrageous," said Strobe Talbott, a former deputy secretary of state now at the Brookings Institution, who participated in more than a dozen meetings between President Bill Clinton and then-Russian President Boris Yeltsin in the 1990s. "It handicaps the U.S. government - the experts and advisers and Cabinet officers who are there to serve [the president] - and it certainly gives Putin much more scope to manipulate Trump."