In short, Putin can do no wrong nor can Russia in Trump's eyes. When the Russian president ordered the United States recently to eliminate 755 positions at our embassy in Moscow, a retaliatory measure, Trump thanked him.
No one has ever been able to explain why Trump so reverse the intensely corrupt tyrant Putin, who has worked for decades to weaken America. Trump cannot contain his boycrush, even in the face of recent Congressional repudiation of Russia and all the evidence of election tampering and other systematic hacking that endangers America.
At a minimum, such blind adoration makes Trump look like a fool. More troubling, it makes him look like he's been compromised somehow by Putin and responds with sycophantic groveling.