Hence Trump's inaction and disbelief are sending a clear signal to Moscow: Keep it up!
At a minimum, Trump is taking this stance because, to admit interference was and is a real threat, it somehow deligitimizes his winning the White House.
At worst, it means Trump is a willing agent of Moscow and is happy to undermine American democracy.
Either option is horrible. And tragically Republicans in Congress will continue to look the other way because they think it benefits their party, thus putting politics before country.
The White House is occupied by a quavering coward and protected by corrupt enablers on Capitol Hill. What a sorry state of affairs.