When Donald Trump addressed the nation on Monday night, presenting his Afghanistan strategy, he admitted that it was likely to disappoint his supporters.

Mr Trump has long championed withdrawing from Afghanistan, repeatedly attacking Barack Obama for the continued US presence in the region.

Yet in a surprise move on Monday night, he claimed that a withdrawal of personnel would leave a power vacuum that to be filled by terrorists, as has happened in Iraq, and committed to more troops.

In August 2010 US troop numbers peaked at 100,000, but Mr Obama, despite repeated efforts to withdraw, failed to completely exit the country.

He handed over to Mr Trump with 8,400 troops. “My original instinct was to pull out - and, historically, I like following my instincts,” he said. 

“But all my life I've heard that decisions are much different when you sit behind the desk in the Oval Office; in other words, when you're president of the United States.” 

As ever with Mr Trump, his tweets came back to haunt him.

In 2011 Mr Trump appeared on the show of his friend, Bill O'Reilly, on Fox News.

"What I'm getting from you, though, is you would withdraw US troops out of Afghanistan?" asked O'Reilly.

Mr Trump replied: "Yes, I would."

O'Reilly asked whether they would mean the return of the Taliban.

"Well, they're going to come back anyway because they're really in Pakistan," said Mr Trump.

Five years to the day before his Fort Myer speech, Mr Trump tweeted: “Why are we continuing to train these Afghanis who then shoot our soldiers in the back? Afghanistan is a complete waste. Time to come home!”

A year later, in 2013, he continued his theme, stating: “Let’s get out of Afghanistan. Our troops are being killed by the Afghanis we train and we waste billions there. Nonsense! Rebuild the USA.”

In March 2013 James Mattis, Mr Trump’s current defence secretary, who at the time was the general leading the US military's Central Command, said that he recommended keeping 13,600 American troops in Afghanistan after 2013.

Mr Trump disagreed, tweeting: “We have wasted an enormous amount of blood and treasure in Afghanistan. Their government has zero appreciation. Let's get out!”

In November 2013 Mr Obama again promised to bring the conflict to an end. "This winter, our troop levels in Afghanistan will be down to 34,000, and by this time next year, the transition to Afghan security will be nearly complete. The longest war in American history will end," he said.

He announced that instead of dropping the US troop level to 5,500, he would keep it at about 8,400 through the end of his term, saying his successor can determine the next move.

Afghanistan barely registered during the 2016 election campaign. But, before taking the reins of power, Mr Trump continued to talk in vague terms about reducing US presence.

He said at a December 2016 “thank you rally” in North Carolina that the policy of "intervention and chaos" must come to an end.

Yet on Monday he had changed his mind and committed more troops to Afghanistan. “The consequences of a rapid exit are both predictable and unacceptable,” he said.

“A hasty withdrawal would create a vacuum that terrorists, including ISIS and al Qaeda, would instantly fill.”

 Mr Trump coupled his pledge with a demand for countries like Britain to do more and criticised Pakistan for not doing enough to tackle terrorist "safe havens".

"Pakistan has much to gain from partnering with our effort in Afghanistan. It has much to lose by continuing to harbour terrorists," he said.

He also warned the Afghan government that it should not view US support as a "blank check" and said America would work with them "as we see determination and progress".