Donald Trump wasted no time in making a lofty promise at the Republican convention:

"The crime and violence that today afflicts our nation will soon--and I mean very soon--come to an end," and the day he is sworn in, "safety will be restored."

He cannot keep that promise, of course, but it's not meant to be taken literally. Like so much in the Trump persona and candidacy, he promises greatness, details be damned, and his supporters respond to the aspirational bluntness.

If I had to pick a signature line in the oration that roused the crowd here in Cleveland, it would be this, about "people who work hard but no longer have a voice. I am your voice."

It was an attempt to fuse his loud, rough-edged and sometimes divisive voice with the needs of ordinary folks.

What seemed so ludicrous to so many a year ago, that this bombastic billionaire and New York street fighter would be accepting the Republican nomination, also created for him a special challenge. A man who loves to riff and joke and feed off the energy of crowds, he was reading the ultimate scripted speech. There was little levity and only a few personal lines, about his parents and late brother. Trump was all business, and his mission was to persuade wavering voters that he has the depth and discipline to run the country.

In short, to pass the commander-in-chief test.

Trump larded the address with attacks on Hillary Clinton, calling her a "puppet" of big donors and ripping her record on such issues as trade. He denounced President Obama for "irresponsible rhetoric."

He hit his marks on such signature topics as immigration and terrorism.

But Trump also sounded notes that are muted for many Republicans. He spoke of nearly four in 10 African-American children living in poverty, and 43 million people on food stamps. He mentioned Ferguson.

And Trump even made a pitch to sway backers of Bernie Sanders, painting him as another victim of a rigged system--a Republican appealing to followers of a self-proclaimed socialist.

He was reading the ultimate scripted speech, and a very long one at that.

For Trump to win with an electoral map tilted against the GOP, he has to peel off enough Democratic and independent voters.

Given his high negatives, Trump's speech was about more than facts and figures. It was about earning trust, despite his lack of political experience.

As the pundits pick apart the speech and replay the sound bites, he may or may not get a bump in the polls. But this was the businessman's best shot, with his biggest audience, to close a deal that at the moment remains in doubt.

Howard Kurtz is a Fox News analyst and the host of "MediaBuzz" (Sundays 11 a.m. and 5 p.m. ET). He is the author of five books and is based in Washington. Follow him at @HowardKurtz. Click here for more information on Howard Kurtz.