Donald Trump participates in the first general-election presidential debate. (Win McNamee/Getty Images)

Search for "30 years" in a transcript of the first general-election presidential debate of 2016. What you'll find — I know because I did it — is five occurrences, all within the first 20 minutes (or so) of the exchange. And that, in a nutshell, is why Donald Trump lost the debate.

Let me explain. Trump came into the forum with a clear game plan: paint Clinton as a longtime Washington insider who hasn't done anything to fix the major problems facing the country — and has, in fact, made them worse, over her three decades in the public eye. And, for a while — a short while — he did it. Here's Trump bashing Clinton on trade:

And, Hillary, I'd just ask you this. You've been doing this for 30 years. Why are you just thinking about these solutions right now? For 30 years, you've been doing it, and now you're just starting to think of solutions.

That's a VERY good message for Trump. If most elections are, fundamentally, a choice between change and more of the same, casting yourself as the change agent and your opponent as the status quo is sound strategy. That's especially true in an election climate like this one in which voters loathe Washington and want to get rid of anyone even marginally associated with it. Just 3 in 10 people in the latest NBC-Wall Street Journal poll said the country was headed in the right direction; a near majority (49 percent) in that same survey said that they preferred "someone who will bring major changes to the way government works even if it is not possible to predict what those changes will be."

Then, suddenly, Trump's winning message was gone. Trump never uttered the words "30 years" for the remainder of the debate — well more than an hour of airtime with an estimated 80 million to 100 million people watching.

What happened? What seems to always happen to Trump: He got distracted by Clinton's attempt to lure him into fights — birtherism, tax returns, the war in Iraq — that he simply couldn't win. I watched the minutes roll by as Trump tried to explain why it made perfect sense that he hadn't filed his tax returns or why he had somehow been proven right on birtherism. And with every passing minute, Trump got further and further away from the case he needed to make in this debate: She's the insider. I'm the outsider. If you want change, vote for me.

Trump's biggest problem in this campaign is his lack of discipline. While his freewheeling, seat-of-the-pants style worked for him during the Republican primary, it has betrayed him at times in the general-election contest. To win a general election — particularly given the demographic and electoral map challenges Trump faces — you need to use each of the three debates to prosecute a case against your opponent. To do that, you need to avoid the traps he (or she) sets for you.

Trump didn't — and, I think, can't — do that. He has said any number of times that if someone punches at him, he has to answer back. That's fine if you are a businessman and reality TV show star. Heck, it's probably good for business. But in politics, message discipline matters a lot. Most people pay only passing attention to politics and so you need to say the same thing again and again (and again) before it starts to penetrate into people's consciousness. So if you want to drive home the idea that Clinton spent 30 years in Washington not fixing problems, then you need to say it a lot more than five times in the entire debate.

Trump appears to have gotten that message — again! -- from his political team overnight. Here's his tweet from this morning on that subject:

Too little, too late. If Trump wants to make the argument that Clinton's three decades in Washington are fundamentally disqualifying in this change-oriented political environment, he just blew a major opportunity to prosecute that case on Monday night.