Trump was not the one who chose Oz to run. It was the voters in PA. If Trump had not endorsed Oz and Oz lost , folks would be blaming Trump for not endorsing him.
Oz was losing the entire primary until Trump endorsed him... Trump owns some very larger responsibility for the OZ fiasco.. and even with OZ’s endorsement he just barely won the primary...
OZ fiasco isn’t fully Trump’s fault, no but he has culpability, as to Hannity and the establishment GOP for their ruthless attempt to destroy Barnette when she became a real threat.
No Trump isn’t solely responsible for the Oz fiasco, but he absolutely has culpability in it.