Editors' pick: Originally published March 15.

Last Thursday marked the first time that a Republican primary debate in this election cycle was more about issues than about personal attacks. Why the sudden shift to substance?

Because it's in Donald Trump's best interest.

In pastarticles, I've noted that watching Trump smash the Republican primaries calls to mind a poker player type that is difficult to handle in tournaments: the "loose-aggressive" player, or LAG. The LAG is hyper-aggressive. She makes it hard for other players in a poker tournament to win pots because she tries to win them all. If you bet, then the LAG raises. If you re-raise, then the LAG bets all her chips. Donald Trump is a LAG and the U.S. presidential election is the highest stakes poker tournament of all time.

Through his LAG style of never backing down, Trump has managed to accumulate a massive chip lead in the Republican primary, and with that massive chip lead, he needs to start thinking about winning the whole poker tournament (the general election). So, during Thursday's Republican debate, he did what we in poker call "changing gears."

In poker, "changing gears" is a sudden shift in tactics. Once opponents at the table know they are dealing with a LAG, they can take steps to try to defeat the LAG. But if the LAG changes her tactics, her opponents may again be fooled. Changing gears at just the right time can be a hugely successful move for a poker player.

Now that Trump is comfortably ahead, he no longer needs to repeatedly attack the other candidates, especially now that they (mostly Florida Senator Marco Rubio and Texas Senator Ted Cruz) have changed tactics themselves and started challenging Trump more consistently as he nears securing the nomination. In the penultimate GOP debate, Trump the LAG faced the only thing that a LAG hates: His opponents matching his aggression with their own. That debate was a bloodbath, with both Trump and his opponents throwing -- and landing -- massive blows.

Rubio and Cruz, seeing the end near, were no longer letting Trump win most of the pots with his aggression. Rubio, in particular, let loose a furious salvo of attacks.

But when Rubio and Cruz switched tactics, it was the perfect time for Trump to switch tactics as well. And in Thursdays debate we saw exactly that. Trump started talking issues and attacked a lot less. He even spoke of uniting the Republican party after a brutal primary battle. Trump went from playing his game of insulting and never backing down to talking issues.

Even though Trump isn't as good at this style of campaign as Rubio or Cruz (they have vast experience and practice), the tactic worked beautifully. There were no ugly confrontations in this final debate like there had been in previous contests. And, at this point, with his huge lead, that's how Trump wants it. He may have lost a few points on policy here and there, but going into some of the biggest state primaries this week (Ohio and Florida, where his wins would all but assure the nomination) he's still well in the lead and set to secure the GOP nomination.

In the primary, Trump built a huge lead with the hyper-aggression of the LAG. Then, when the time was right, he shifted gears, outmaneuvering his opponents when they were at their most desperate. And now he's about to do the unthinkable and ride these successful tactics to the Republican nomination.

And it didn't hurt that he spent one debate practicing sticking to the issues; that practice will serve him well when he faces Hillary Clinton on the debate stage in the general election.

This article is commentary by an independent contributor. At the time of publication, the author held TK positions in the stocks mentioned.