Sen. Marco Rubio (R-Fla.) had a good week, building on last week’s strong debate performance. He did it by showing moxie and by simultaneously highlighting Donald Trump’s worst quality: He is a terrible cry baby.

Trump, sensing the threat from Rubio, started in which his usual attacks, insulting everything from his hair to his perspiration under the debate lights. Rubio, showing aggressiveness Jeb Bush might lack, hit him squarely on the jaw: “He had a really bad debate performance last week. He’s not well informed on the issues. He really never talks about issues and can’t have more than a 10-second soundbite on any key issue. And I think he’s kind of been exposed a little bit over the last seven days, and he’s a touchy and insecure guy and so that’s how he reacts, and people can see through it.” That succinct statement had the benefit of being true.

Many conservative critics have been slamming Trump for whining about Fox News coverage and lashing out whenever someone (in the media or the field) gets the better of him. (Charles Cooke called him “a preposterous little trust-fund wuss. . . . As was illustrated once again last night, the man is not really a ‘fighter’ or an ‘alpha male’ or an iron-cored ‘enemy of political correctness.’ He’s a thin-skinned performance artist whose peculiar shtick falls to pieces the moment someone useful elects to return a punch.”) In swift order, Rubio not only showed some muscle of his own but also emphasized Trump’s weakness. It was a bit of political jiu-jitsu that cheered many conservatives who have had enough of Trump.

That said, Trump is right in one regard: Rubio will need to show he is mature enough and experienced enough to be president. Given that three contenders have zero experience, the freshman senator and former Florida state house speaker may have all the training he needs. Right now, Rubio is winning converts in part because he has something meaningful to say. Today at the Value Voters Summit, for example, he rolled out a new initiative:

I will provide a limited 25% non-refundable tax credit to any business that offers between four and twelve weeks of paid leave. For instance, if you are offered $1,600 in paid leave for four weeks while you take care of your newborn, which would be the equivalent of about $10 an hour, your employer could claim a tax credit for $400.
This won’t solve every scheduling conflict between work and family life. No policy can. But it will help ensure that our people don’t have to sit behind a desk while the most profound moments of their lives pass them by. And it will help our businesses expand and create new jobs by allowing them to keep more of their money rather than send it to Washington.

Libertarians and those pushing a bare-bones flat tax won’t like this, but it does respond to the voters’ desire for government that solves their issues. Likewise, his tax plan, his campaign reminds us in an e-mail, contains several family-friendly items:

  • Create an additional $2,500 child tax credit to provide relief to middle-class families.
  • Eliminate the marriage penalty.
  • Cut taxes for businesses of all sizes to no higher than 25 percent.

This, he promises, will boost wages and jobs.

Rubio has an agenda with plenty of innovative ideas. His biggest test, however, will be to convince voters he’s ready to take on the Democrats and international foes such as Vladimir Putin. Knocking Trump down to size is not quite the same thing, but it is a good start.