First Trump marginalized the intelligence agencies' conclusion as "could have been a guy in New Jersey."
Then he concluded that Russia wasn't involved and made the issue political even to the point of calling it a "witch hunt."
Trump even gave more credit to Assange than the US Intelligence agencies.
Now he that was briefed with classified information he does nearly a complete 180 and promises to act in the next 90 days to address cyberwarfare.

Judging from Trump's conduct he is making public judgments he is completely clueless about.  What's worse is that he knows of his own ignorance and yet still opens his mouth and proceeds to stick his foot in.  Trump complained about the CIA being involved with the Iraq invasion but at least Bush acted with some information in reaching a conclusion.  Trump's conclusion without any information, willful disregard for any evidence to the contrary and intentional attacks on intelligence agencies is far, far worse.