John McTernan is a former speechwriter for ex-British Prime Minister Tony Blair and ex-communications director to former Australian Prime Minister Julia Gillard. The opinions expressed in this commentary are his.

Even as President-elect, Donald Trump has not stepped back from Twitter.

(CNN) Why does he keep on doing it? Why does Donald Trump keep on tweeting?

Some people had thought that as the transition process started and the reality of becoming the most powerful man in the world loomed ever larger, the President-elect's habits would change.

They have received a short, sharp lesson that in politics -- as in life -- you should never believe in what you hope for.

Not only have the tweets continued, they have also not moderated one bit.

Just take the last week or so.

We should tell China that we don't want the drone they stole back.- let them keep it! — Donald J. Trump (@realDonaldTrump) December 18, 2016

What is going on?

Now political staffers know the drill with senior politicians and Twitter.

• Rule 1 is don't let them tweet.

• Rule 2 is change their passwords -- and don't let them know it.

• Rule 3 is if in doubt, refer to Rule 1.

Easy to say, but hard to do -- yet it is essential.

In traditional politics the price for "misspeaking" is high -- gaffes, splits, flip-flops are usually deadly for credibility and thus for poll ratings.

Not so for Trump. The lower he went, the higher he rose.

With Twitter, Trump found a short, fast, immediate and direct way to communicate.

George Burns' famous saying about sincerity -- "if you can fake that, you've got it made" -- has often been applied to politics.

This year -- with the rise of Nigel Farage in the UK, Brexit and the election of Trump -- has taught us that authenticity is now the currency of politics.

This year -- with the rise of Nigel Farage in the UK, Brexit and the election of Trump -- has taught us that authenticity is now the currency of politics. John McTernan

The secret to Trump's success is breathtakingly simple.

He became a celebrity through television and, in particular, through the emerging genre of reality TV.

He realized that celebrity conferred authority, and that while this was usually turned to commercial advantage, he could broker celebrity into political authority.

But why Twitter?

His genius was to find a channel -- a medium -- through which to communicate: Twitter.

It's short, fast, immediate and above all direct and unmediated.

What you see is what you get -- and that cuts through.

Media professionals too often focus only on the message they are sending and forget the thousands of messages that are bombarding the public daily.

Most people screen out most of what is aimed at them, whether it is advertising or political messaging.

But they can't ignore conflict.

Just as drivers on a freeway can be found rubbernecking at a car crash, so Twitter users are drawn to a fight.

And boy, does the President-elect relish those.

It shouldn't have been a surprise.

Remember Roosevelt?

Mastery of the medium is the key to political dominance.

President Franklin D. Roosevelt was the king of radio -- it was the most important medium of his time.

Mastery of the medium is the key to political dominance. John McTernan

Similarly, from abandoning his hat for a cleaner, crisper image to triumphing in a televised debate, President John F. Kennedy was the master of television.

Again, winning in the dominant medium of the time was the key to victory. Now we have Trump.

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Even in a fragmented media landscape there is a single channel that can matter more than the others.

David Plouffe once said of President Barack Obama's nomination and election that there was "a narrow path to victory."

Nothing could be narrower than 140 characters, nothing could be wider than the impact of becoming the master of Twitter.