The Washington Post explains in great detail President Trump's problematic approach to Russia and the danger his refusal to accept election interference as fact poses to the United States and its national security. It is a long read but worth the time:
Nearly a year into his presidency, Trump continues to reject the evidence that Russia waged an assault on a pillar of American democracy and supported his run for the White House.
The result is without obvious parallel in U.S. history, a situation in which the personal insecurities of the president — and his refusal to accept what even many in his administration regard as objective reality — have impaired the government’s response to a national security threat. The repercussions radiate across the government.
Rather than search for ways to deter Kremlin attacks or safeguard U.S. elections, Trump has waged his own campaign to discredit the case that Russia poses any threat and he has resisted or attempted to roll back efforts to hold Moscow to account.
Full read: Doubting the intelligence, Trump pursues Putin and leaves a Russian threat unchecked (WaPo)