BRIDGEWATER, N.J. — President Trump late Saturday tried to explain his slow and unsteady walk down a ramp at the U.S. Military Academy at West Point, which had generated concern and mockery on social media, by claiming the walkway was "very slippery" and that he was worried about falling.

The walk in question came at the conclusion of Saturday’s commencement exercises at West Point, where Trump was the guest speaker. As he exited the raised platform by descending a ramp alongside Lt. Gen. Darryl A. Williams, the academy’s superintendent, Trump was visibly tentative and took short, careful steps.

Video of the moment was widely shared on social media, with critics of the president — including Republican operatives working on the Lincoln Project, an anti-Trump group whose ads have provoked the president’s ire — using the hashtag #TrumpIsNotWell in their tweets.

The chatter seemed to get the attention of Trump, who is spending the weekend at his golf club in Bedminster, N.J. At 10:57 p.m. Saturday, the president wrote on Twitter: “The ramp that I descended after my West Point Commencement speech was very long & steep, had no handrail and, most importantly, was very slippery. The last thing I was going to do is ‘fall’ for the Fake News to have fun with. Final ten feet I ran down to level ground. Momentum!”

Elements of Trump’s explanation strained credulity. Trump’s claim that the ramp had been “very slippery” was inconsistent with the weather, which on Saturday in West Point, N.Y., was sunny and clear-skied. The grass plain on which the commencement took place was dry.

In addition, Trump wrote that he “ran down” the final stretch of the ramp. Video footage of the episode shows the president picking up his pace slightly for the final two steps, but that would hardly be considered a run or a jog by any standard definition.

Once on flat ground, Trump appeared to walk normally as he surveyed the field and mingled with officers on his walk to board Marine One, which was parked roughly 100 yards or so from the platform stage.

The ramp video was not the only clip from Trump’s speech to generate considerable attention on social media. Another was when he briefly took a sip of water while standing behind the presidential lectern. As Trump raised a small glass of water toward his mouth with his right hand, he used his left hand to steady the bottom of the glass so he could take a sip.

Trump is exceptionally attuned to — some advisers say obsessed with — the image he presents to the public and strives to be seen as strong and vigorous.

Trump, who is celebrating his 74th birthday on Sunday, has long sought to create an impression of himself as having supernatural stamina. This was a contrast he tried to make with his 2016 Democratic opponent, former secretary of state Hillary Clinton, and again with his presumptive 2020 Democratic rival, former vice president Joe Biden.

Trump routinely mocks Biden as “Sleepy Joe” and has tried to argue that Biden, 77, lacks the physical or mental acuity to be president. But Trump’s critics seized on Saturday’s ramp walk to turn the tables on the incumbent, recirculating video clips on Twitter of Biden jogging along a parade route and down the White House Colonnade with then-President Barack Obama.