Did you take the birthers seriously? No, you didn't.
Because it was easily disproved. That Putin has been puppeteering Trump, however, is not easily disproved. There is in fact significant evidence that exists to suggest Putin is the one calling most of Trump's shots, particularly when it comes to foreign policy.
If not to the level of the kind of conspiracy you're talking about, certainly along the lines of Trump openly admiring Putin and siding with Putin over our own intelligence community and basically publicly and privately sucking his cock over and over and over again, where it is not out of the question
at all that if he called Putin and asked him what he would do, Trump would do whatever Putin would do.
The comment to which you were responding was, after all, simply this:
I assume he checked with Putin, who nixed it...
That does not necessitate a flat-earth-level conspiracy and is in perfect line with pretty much everything Trump has ever done or said in relation to Putin.