It does, FROM A CERTAIN PoV, not matter whether this guy was Islamist, or Christian or whatever.
It does not matter whether he was an Islamist because no measure, no "banning of Muslims entering the country", no "bombing of ISIS" or not letting in refugees into the country can prevent that someone is a nutter, whether Islamist or nutter Christian, shooting up innocent people, for whatever reason.
Even TEN Trumps as president could not have prevented someone born in the US, becoming Muslim...and go on a killing/hate spree....and it does in-fact MATTER ZERO whether someone "supports letting in immigrants" or not.
In-fact, if anything, this should show to you and anyone else how pointless it would be for preventing terrorism to "not support letting in Muslims"..it would have done SHIT in this case....in the same way as your wall would do SHIT to bring back jobs.