When Donald Trump began tweeting in 2009, his feed was mostly just a home for notable quotes from his books about how to succeed in business.

In less than 140 characters, one 2009 missive sums up most of the 30,000 others that followed: “Keep it fast, short and direct — whatever it is.”

With Twitter, Trump — known as a master marketer in the real estate and entertainment world — has met his medium. Just as he stamps his buildings and properties around the world with his name, each Trump tweet is branded with his name and likeness and sends a clear signal to the political world about what he wants them to know.

Trump has thrown out the traditional social media handbook and replaced it with his own unmistakable flair. There are few hashtags or photos to catch the eye, only outrageous statements and exclamation marks. Trump rarely vets the content he retweets, largely ignoring established brands, preferring instead to amplify the voices of real people.

Those decisions have made Trump’s Twitter feed both unmistakable and polarizing.

During the campaign, he retweeted the accounts of white supremacists and after the election, expanded on his feud with CNN reporter Jeff Zeleny by retweeting @Filibuster, a user whose profile identifies as a 16-year-old boy.

“Pathetic - you have no sufficient evidence that Donald Trump did not suffer from voter fraud, shame! Bad reporter,” he wrote of Zeleny, quoting @Filibuster.

The story might have ended there, as unconventional as it was. But Trump, who otherwise does not use computers or email, had magnified this tweet in his unusual way, bypassing the retweet function and instead copying and pasting the 16-year-old’s message and adding his own quotation marks.

Except that he had forgotten to close the quotation, making it impossible to tell where Seth’s thoughts ended and Trump’s began.

Later, Seth complained that he was being unfairly blamed for the “Bad reporter”part. That had come from Trump.

“Trump knows how to build a brand and has proven over time that he can really do it,” said Tim Calkins, a professor of marketing at Northwestern University’s Kellogg School of Management. “A brand has to stand for something. A brand cannot be all things to all people.

“Trump is very comfortable with being polarizing. And he’s comfortable with his brand being polarizing.”

Since he became a candidate for president, the tweets posted from Trump’s Android cellphone have come fast and furious. They are often directed squarely at a person or a thing that has crossed him.

Data scientist David Robinson analyzed thousands of Trump’s tweets and found that the ones he wrote were far more likely to use words associated with disgust, anger, fear and sadness than the tweets written by his staff. And in general, they were more negative than the generic tweets written by his staff. (Tweets written by Trump come from his Android, while his staffers’ tweets come from an iPhone or other devices.)

When he becomes president, none of that is expected to change. He is likely to continue tweeting as he has during the campaign and the transition.

He is most likely to tweet early in the morning and late at night, and the words at those times are his and his alone. He types them out or dictates them to an assistant, viewing them as a direct line to his supporters.

At other times, he might confer with aides on the language — channeling his preference to attach negative adjectives, such as “failing,” “overrated” or “dishonest” — to his adversaries.

Invariably, Trump’s combative approach helps his tweets spread far and wide — with far more impact than his Democratic or Republican political opponents, according to one study.

That Pew Research Center study found that during a three-week period during the presidential campaign, Hillary Clinton’s tweets got less than a third of the retweets that Trump’s did.

Clinton used Twitter to distribute links, images and videos and to engage with other well-known accounts. But Trump’s didn’t bother. His messages were far more likely to be plain text, often in all caps.

The words don’t just ricochet across the Internet, they are also immediately written and talked about in traditional forms of media, including television and print.

“It’s magnification,” said former Trump adviser Corey Lewandowski, describing the intended effect. “People tweet stuff all the time, but they don’t have the reach that he does because of the media.”

Trump has a finely tuned sense of the perfect tweet, and its goals are simple: skip the filter.

“Trump understands the power of going directly to the people, and that’s what he does,” said Lewandowski.

Opposing primary campaigns learned early on that when Trump tweeted, the day was essentially over.

He labeled his opponents “Little Marco” and “low energy” Jeb Bush. He picked fights with political figures and laymen.

But whether the tweets resulted in good news or bad news, the effect for his political opponents was the same. “His tweets would drive a news cycle,” said Alex Conant, a former communications director to Trump’s primary opponent Sen. Marco Rubio. “His very efficient and effective way of dominating the conversation on Twitter is something no campaign could compete with.”

In the transition, corporations braced for a scolding on social media. And foreign governments monitored it closely for clues about his thinking on issues as consequential as the world’s nuclear arsenal.

“The United States must greatly strengthen and expand its nuclear capability until such time as the world comes to its senses regarding nukes,” Trump tweeted on Dec. 22.

The message sent the media and political world into a tailspin, as seemingly everyone in the world scrambled to figure out what he meant.

Sometimes, his missives leave even his own staff wondering.

Trump’s pick to be his White House press secretary, Sean Spicer, said that when his boss tweets, he often learns about it when everyone else in the world does.

“I do not know, I do not get a memo,” Spicer said at a University of Chicago Institute of Politics event. “He drives the train on this.”

When Trump is in the Oval Office, however, the stakes will be higher than ever.

“There’s not much room for unforced errors when you’re president,” Conant added.