The whole idea that Obama's vetting offers an excuse seems irrational in the first place .... given that the payments the Turks and Russians made to Flynn occurred after he was fired by the Obama administration.
In Trump's buck pass, was Obama meant to predict that Flynn would one day solicit payments from Russia and Turkey after he lost his job? Or is he claiming that Obama's team was required to vet people who don't work for the government any more?
What this new information seems to suggest is that Trump is trying very hard to protect Flynn. This could be loyalty; but although Trump requires loyalty he has shown no signs of offering it. So the more likely explanation is that Trump knows that Flynn is a liability in the Russia investigation and he is desperately trying to prevent him from revealing his knowledge.
Trump surely knows that Flynn was vetted. I guess he knows his Fox News audience will buy any explanation he offers.