Donald Trump seems to have skipped a crucial step in preparing to run for President. And it could be his undoing.

Courtesy of Mother Jones:  

For most major presidential campaigns, it is a routine act: You conduct opposition research on your own candidate. The reason is obvious; campaign officials and candidates want to know what they might have to contend with once the you-know-what starts flying. But not Donald Trump. At least not at the start of the campaign that would lead to him becoming the presumptive GOP nominee. According to a source with direct knowledge, when Trump was considering entering the presidential race early last year, his political advisers, including Corey Lewandowski, who would become his campaign manager, suggested that he hire a professional to investigate his past. But the celebrity mogul said no and refused to pay for it. 

Marital infidelity, connections to mob-related persons, bankruptcies, the hiring of undocumented workers, policy flip-flops, deals gone bad, legal troubles—Trump's life is an opposition researcher's dream. That was no secret to his political lieutenants, who prior to his announcement discussed the need to conduct a deep dive into the tycoon's background. The point was to do more than Google searches and perusing of the many books written on Trump—and to instead mount a full forensic examination of everything Donald. Especially before anyone else did. (Trump's aides had heard a rumor that wealthy conservative donors, perhaps including the Koch brothers, were underwriting a private opposition research effort aimed at the former reality TV star.) 

"Everyone does this," says a former Mitt Romney aide. "I don't know a campaign that didn't. It's a standard procedure." Political research firms specialize in this sort of work. "It's an off-the-shelf service they provide," this aide notes. "For X dollars, you get a different level of digging. I've never known a campaign that didn't do this. After all, you're expected to know your own record. Any responsible campaign would do that."

I think the key phrase here is "responsible campaign." 

Let's face it Trump is an "in the moment" kind of guy who can say today today the exact opposite of what he said in the past, such as he recently did concerning Libya, and expect nobody to call him out over it.

The problem for Trump is that the Clintons are experts at oppositional research and if there are smoking guns to be found, they will in fact be found.

Their challenge is in making sure that it actually sticks to Trump and makes it harder for people to justify voting for him. So far nothing that we know, and we know a lot, seems to have accomplished that feat.