Donald Trump’s next move: Attack Hillary Clinton to win GOP nomination

With yet another night of big primary wins behind him, Donald Trump may actually be able to defy the odds makers and secure the 1,237 delegates he needs to win the Republican presidential nomination on the first ballot at the convention in Cleveland. But, there's one thing Trump needs to do to solidify his existing support, win over many of the Republicans still objecting to him and clinch the nomination without a convention fight.

That thing is simply to start attacking Hillary Clinton, and only Hillary Clinton, from now until that convention and beyond. It's such a simple, no-brainer strategy that it's downright hard to understand why Mr. Trump didn't enact it as his sole focus months ago. Even after last night's victory, he's still spending most of his considerably large amount of daily free TV air time bashing Ted Cruz. This may be just as much of a reason that Trump has lost more than two dozen national polls to Mrs. Clinton as his comments about immigration and women.

Donald Trump and Hillary Clinton, presidential candidates
Donald Trump and Hillary Clinton, presidential candidates

Trump may be cashing in on a number of his unconventional campaign methods, but so far that has mostly been because so many Republicans were in the race. With more than 10 candidates running at the beginning of the process, perhaps we all should have known long ago that the loudest and brashest guy would have a big advantage. But now that Trump has ended the chances of all his GOP opponents, it's long past time for him to act like the nominee and avoid any more scraps with his intraparty rivals. Focusing on how he's being treated unfairly by the party establishment, which has been his #1 message for more than a month, accentuates and reminds every one of the fact that he's not even liked by many in his own party.

But the real reason he should be after Hillary 24/7 is because the few times he has focused on her have produced results. It started in December when he attacked Bill Clinton by basically calling him a sexual predator and Hillary as his enabler. His comments drew an angry reaction from Mrs. Clinton, but they seem to have made the news media shier ever since about gravitating to the still very popular Bill Clinton's campaign appearances.

And for more than a week, that one attack kept one of the most ugly chapters in the Clinton family history on the front burner. It also gave pause to a lot of progressive voters who should have flowed into Hillary's campaign army long ago, especially after Trump made his initial misogynistic attacks on Carly Fiorina and Megyn Kelly. Instead, Mrs. Clinton's high negative poll ratings haven't improved and have even risen since that initial December attack by Trump and that's a major reason why the Bernie Sanders campaign has surprisingly endured for so long.

More importantly and more clearly, that attack also boosted Trump's stature among the considerable portion of Republican voters who have had a seething distrust, dislike, or just plain hatred for Hillary Clinton since 1992. Even the most anti-Trump GOP voter has a visceral problem with Mrs. Clinton. Attacking her, especially in the uniquely caustic Trump way, will drag a lot more of the non-Trump Republican voters into his campaign than it will drive away. And you don't need a Ph.D. in political science to know that.

But even though Trump briefly scoffed at Clinton's gender-based campaign last night, and he doubled down on it after being goaded by Good Morning America anchor Chris Cuomo this morning, he's still curiously keeping almost all of his powder dry against his presumptive general election foe. Just look at Trump's infamous Twitter feed and you'll be hard-pressed to find any mention of Mrs. Clinton at all. When you do find one, it's almost never without it also being a part of an attack on Senator Ted Cruz or another Republican rival. We can argue about whether most voters like a really nasty campaign, but it's not debatable that if Trump wants more GOP support, he should direct that nastiness against a Democrat who makes just about every Republican's skin crawl.

We can speculate about why he hasn't made this no-brainer decision. One reason is that while born to great wealth, Trump is still such a street fighter at heart that he cannot divorce himself from any scuffle no matter what the bigger picture. As long as Cruz and Governor John Kasich are still in the race, Trump doesn't seem able to resist bashing them. Another possible reason is that Trump has famously not been advised or just hasn't been listening to true campaign professionals until recently. No one with any political campaign managing experience above a race for dog catcher would advise Trump to keep bashing his GOP rivals, but then again it seems like hardly anyone has been advising him at all.

Hillary Clinton has made similar mistakes. Her campaign does best when it focuses on all the things about Donald Trump that anger and scare core Democratic voters. She started to do that again today on her social media feed and I doubt she will mention Senator Sanders much in the coming days, if at all. The surprising strength of the Sanders campaign and constant claims that the entire Democratic race has been rigged from the start succeeded in getting the Clinton camp to take its eyes off the general election ball for a few months, but the professionals on her campaign team will fix that now.

And so every day that Trump continues to spend time on intramural attacks rather than bashing Mrs. Clinton should tell Republicans and all voters two important things: first, that Donald Trump is weakening his own chances to win the White House, and second, this is not and never has been a serious campaign at all.

Commentary by Jake Novak, supervising producer of "Power Lunch." Follow him on Twitter @jakejakeny.

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