WASHINGTON (Reuters) - Under pressure from gun rights groups, President Donald Trump backed away on Monday from raising the minimum age for gun purchases from 18 to 21, one of several measures he had supported after the latest U.S. school shooting.

The proposal to raise the minimum age for buying guns from 18 to 21 was not part of a modest set of Trump administration school safety plans announced on Sunday and which were closely aligned with National Rifle Association (NRA) positions.

The administration plan also included training teachers to carry guns in schools, an idea already in place in some states and backed by the powerful gun lobby.

“On 18 to 21 Age Limits, watching court cases and rulings before acting. States are making this decision. Things are moving rapidly on this, but not much political support (to put it mildly),” Trump wrote on Twitter.

Florida last week adopted new gun regulations, triggering a federal lawsuit from the NRA to block raising the minimum age for buying long guns.

The Republican president, who championed gun rights during his 2016 campaign, vowed to take action to prevent school shootings after a gunman killed 17 students and faculty at a high school in Parkland, Florida, on Feb. 14.

The shootings reignited fierce debate in the United States, and Trump stunned members of Congress during White House meetings by endorsing proposals long opposed by his fellow Republicans and accusing lawmakers of being afraid of the NRA.

However, the measures proposed by the White House on Sunday night were weaker than some of the more sweeping changes Trump had embraced during his televised meetings on the issue.

White House spokeswoman Sarah Sanders said Trump still backs some of those changes, including new age limits, but is focusing on measures that can get through the U.S. Congress.

“Right now the president’s primary focus is on pushing through things that we know have broad bipartisan support or things that we can do from an administrative perspective, that we can do immediately,” she said at a news briefing.

Trump backs legislation aimed at providing more data for the background check system: a database of people who are not legally allowed to buy guns. But he did not endorse a broader proposal that would close loopholes in existing law by requiring background checks for guns bought at gun shows or arranged over the Internet.

FILE PHOTO: U.S. President Donald Trump speaks in support of Republican congressional candidate Rick Sacconne during a Make America Great Again rally in Moon Township, Pennsylvania, U.S., March 10, 2018. REUTERS/Joshua Roberts

The NRA did not return a request for comment on the president’s proposals on Monday.

The top Democrats in Congress accused Trump of caving to the NRA and vowed to keep pushing for tougher gun measures.

“The families and students suffering from the heartbreak of gun violence deserve real leadership, not a White House that cravenly tiptoes around the NRA,” House Democratic leader Nancy Pelosi said in a statement.

Trump met with the NRA privately at the White House twice last month as he weighed his response to the shooting.

It was not clear how quickly Congress would move on the issue. Senate Majority Leader Mitch McConnell, a Republican, has not scheduled debate for any gun-related bills.

The NRA-backed background check data bill, which now has a supermajority of co-sponsors, is pending in the Senate. With more than 60 co-sponsors in the 100-member chamber, individual senators would have a hard time slowing or blocking its passage if it were brought up for debate.

CONTROVERSIAL PROPOSALS WAIT

The White House put off some of the more controversial proposals, including raising the minimum purchase age, for further study by a new commission led by Education Secretary Betsy DeVos.

Asked why the age limit proposal was dropped from the administration plan, DeVos told NBC’s “Today” show that the plan was the first step in a lengthy process.

“Everything is on the table,” she said on Monday.

The Justice Department will also provide an unspecified amount of grants to states that want to train teachers to carry guns in school.

In Congress, the House of Representatives on Wednesday is expected to debate a bill that would invest $50 million a year to help education and law enforcement officials reduce the chances of gun violence at schools.

On Saturday, the Justice Department submitted a regulation to ban bump stocks - devices that turn semiautomatic rifles into fully automatic machine guns - that would not require congressional approval. Some gun control advocates worry that the regulation will face legal challenges, and have urged Congress to pass a law instead.