Donald Trump turns 73 next week. (Jim Watson/AFP/Getty)

President Trump’s lawyers reportedly warned him against a blanket ban on transgender people in the military before he made the announcement last month.

Trump enraged LGBT activists last week by announcing a ban on transgender people serving in the US military.

In a string of Twitter posts, the President claimed that the military “cannot be burdened with the tremendous medical costs and disruption that transgender would entail”.

The decision, which was allegedly made to appease anti-LGBT Republican lawmakers, has distressed the thousands of transgender people who are already serving in the armed forces.

According to Politico, lawyers both in the White House and in the Department of Defense warned against the ban, and the backlash it would cause.

The report suggests that the warnings led Trump to Twitter to announce the ban himself.

“The administration had no plan in place, but Trump told others they would have to ‘get in gear’ if he announced the ban first,” according to a White House official reported by Politico.

“He also said the announcement would stop the lawyers from arguing with him anymore.”

A poll earlier this week found that a majority of military families oppose the ban.

The Admiral of the US Coast Guard earlier this week said he would defy the ban, and said he had personally spoken to all out trans members of the Coast Guard.

Despite the assertion that it would cost the military too much to implement a transgender-inclusive policy, the Department of Defense spent five times more on Viagra in 2014 than it would on care for transgender troops.

Out trans former Navy SEAL Kristin Beck challenged President Trump to tell her to her face that she is “not worthy” after he announced the policy.

She also noted the negligible cost of providing the healthcare to trans troops compared to other military costs.

According to reports, the Pentagon was unaware that Trump was about to announce the rolling back of the Obama-era change.

It is not the first time Trump has gone out of his way to reverse a decision on LGBT rights made by Obama.

The GOP leader has already scrapped protections for transgender school kids, ceased government opposition to state-level anti-LGBT laws, and sought to slash HIV aid funding.

The decisions sour Trump’s previous claims during his election campaign to be a “friend” of LGBT people.

In a speech directly after the Orlando massacre he had claimed: “Ask yourself, who is really the friend of women and the L-G-B-T community, Donald Trump with his actions, or Hillary Clinton with her words.”

He also won endless praise from gay Republicans for waving a Pride flag on stage, while making no pledges on LGBT rights.