There comes a time in every Republican primary where the frontrunner begins to studiously ignore the also-rans and focus on his likely Democrat opponent. Knowing when to do that is a key skill for any Republican candidate.

Rudy Giuliani did it way too early in 2008, and as a result he never actually won against his Republican opponents. There’s an argument to be made that Romney did it slightly too early in 2012, and that this cost him a much more difficult road to the nomination. Most other Republican frontrunners have known, just by instinct, when it is time to stop attacking your primary opponents and pretend like this thing is over, and let nature take its course.

Trump had that time come and go, at least twice. He had a great opportunity after the March 8th primaries, when he followed up a win on Super Tuesday with impressive wins in Hawaii, Michigan and Mississippi. He had another chance after the March 15th primaries, which knocked Marco Rubio out of contention and in which he won every state other than Ohio.

Either of these wins would have offered Trump a great opportunity to start acting, you know, Presidential, and start a relentless attack program on Hillary, while politely ignoring Cruz and Kasich. Doing so would have made Cruz and Kasich look like ankle-biters, would have helped avert his slide in the head-to-head polling against Hillary, and would have given reluctant joiners reason to hope that a general election matchup between Trump and Hillary might not be a disaster.

Instead, Trump decided to continue his insult comic tour against Cruz, and may have mortally wounded himself in the process. The now-infamous tweet of Heidi Cruz has severely damaged Trump’s ability to consolidate his doubters, especially since there was no reason at all for Trump to have even engaged what a relatively obscure Super PAC said about his wife on a Facebook ad.

His blathering defense of “he started it” has made him sound more juvenile than he already did during this campaign (an accomplishment) and even prompted Anderson Cooper to tell him he was acting like a 5-year-old on national TV. His unforced decision to mock a woman’s looks (for the second time this campaign season) once again brought up the fact that female voters really hate him, and helped further his slide in head-to-head polling against Hillary.

The end result of all this is that Trump’s standing has been harmed – not among his garbage human being dedicated followers, for whom the fact that Trump is a crass lowlife is a feature, not a bug – but with the fence sitting voters who might have been willing to jump in his camp just for the sake of getting this whole ugly primary over with. It’s directly contributed to his ongoing tank job in Wisconsin, which may well serve to blunt his campaign’s momentum going forward.

Right now, Republican voters are talking about a contested convention as a near-inevitability, which it has probably become in spite of John Kasich’s best efforts to the contrary.

And this is all happening to Donald Trump because he is physically incapable of shutting up and not making a horse’s rear out of himself.