On paper, judged by qualifications and career results, the Republican field is very strong. The reason the Republican field is losing to Trump has nothing to do with qualifications. The problem is that once in Washington, Republicans generally lose their nerve. They fear being denounced in the national media, so they cave in to avoid shutting down the government. And when their reasons for shutting down the government prove valid, Republicans don't make their point to the press. In general, Republicans have such fear of seeming strident, they say almost nothing in interviews with the Pravda Press. Trump has shown he does not fear the Pravda Press. That's why he's winning.
Republicans shut down the government in 2013 to get a one year delay for Obamacare. They ultimately failed. When Obamacare rolled out, it was barely functional and obviously not ready for prime time. In short, Obamacare was a disaster. That was the time to link the government shutdown to the one year delay of Obamacare. That was the time to kick the administration for a total lack of judgement. They took a government shutdown so they could roll out an Obamacare system that was obviously not ready, instead of taking a one year delay and getting it right. I didn't see one Republican on any talk or news show explaining that Republicans were right to fight for the delay. Obamacare wasn't ready and would have benefited from a one year delay.
I am not a big fan of Donald Trump in most respects. He's ignorant about checks and balances. He's ignorant about foreign policy. I would strongly prefer several other candidates for Republican nominee. But there is one thing Trump does really well. He makes the Pravda Press dance to his tune, not theirs. In the news arena, Trump is an example of "the heck with them" attitude Republicans need to have at the national level. Republican voters will not nominate another doormat for the Pravda Press to stomp on.