So let’s have a brief look at what US presidents have said about the subject, and what they reportedly knew.
First off there’s been claims by several people that presidents since at least the 60’s aren’t routinely briefed on the topic. If they push hard enough they may get a briefing, but the extent of it varies and that seems to be based on how trustworthy/cooperative the people doing the briefings deem the president in question. Several people have claimed that there has for a long time existed an informal group of people within the government usually referred to as the ”Collin Elite” which is deeply religious and that these people believe that UFOs/aliens are both real and that they are demonic in nature. Supposedly they as a result believe that revealing information about them to the public would somehow enable their demonic plans, and therefore work against disclosure, including informing presidents that they deem aren’t in line with their religious views on the matter. Lue Elizondo has stated that he thought it was a myth until an intel community figure whom he describes as a mentor to him took him aside after he became involved with AAWSAP/AATIP and told him that ”we already know what these are”, that UAPs are demons and threatening him, telling him to stop looking into the matter or unspoken consequences could follow.
The president in recent decades that have been claimed to have been privy to the most details is George HW Bush. He made some eyebrows raise in 2015 when he was doing a fundraiser for Jeb:
During the fundraiser, a man in the crowd raised a strange question which led to an even more surprising response by the former president and CIA director. The man asked George Bush Sr when the US government would tell Americans the truth about UFOs, to which he responded: “Americans can’t handle the truth” before the questioning was briefly halted by organizers of the event.
The man that asked the question has been identified as Adam Guelch, an active member of the Mutual UFO Network (MUFON), which credits itself as being the world’s oldest and largest UFO phenomenon investigative body
Oddly enough, it is not the first time George Bush Sr has had a controversial opinion on the UFO subject as a similar incident occurred on March 7, 1988, during a trip to a George Bush for President Rally in Rogers, Arkansas.
The to-be president was then asked, in the advent that he became president, if he would tell Americans the truth about the existence of UFOs, to which Bush replied: “I am very careful in public life about dealing with classified information” he told the reporter.
James Adder, journalist for the Arkansas Globe at the time, also asked about Bush’s knowledge about the UFO phenomena, on behalf of which Bush answered: ” I know some. I know a fair amount” before ending the interview.
The presumption is that he was briefed in some detail during his stint as CIA director. That stint also ties into another president and what he supposedly knew. Jimmy Carter woved to disclose the truth about UFOs during his campaign, and once elected but prior to inauguration it is claimed that he asked Bush to be briefed on the topic, only to be rebuffed and told that he didn’t have a need to know. Once in office Carter kept pushing to be briefed and eventually the briefing took place. Exactly what was said during the briefing is unclear, as there are multiple stories going around. Apparently a presidential aide came in to see Carter after the briefing and found him sobbing. He did not know what had been said to have caused it though. What is clear is that Carter then declined to disclose information about the UFO issue citing potential national security issues.
Reagan was certainly a believer in the phenomenon, but it seems to be unclear how extensively he was briefed, or even at all. He supposedly made a handshake deal with Gorbachev to ally in the event of an alien invasion, according to Gorbachev anyway:
Shultz was talking about the Lake Geneva summit and mentioned the two leaders ducked out of a meeting to take a walk to a nearby cabin.
"I wasn't there...," Shultz said before Gorbachev cut him off.
"From the fireside house, President Reagan suddenly said to me, 'What would you do if the United States were suddenly attacked by someone from outer space? Would you help us?'
"I said, 'No doubt about it.'"
"He said, 'We too.'"
"So that's interesting," Gorbachev said to much laughter.
But that could have just stemmed from his personal belief in the phenomenon.
Clinton reportedly tried to get briefed and expressed interest in public but it is said that he never was. Something that jives with his later public statements to the effect that if they’re real he wasn’t told about it.
George W Bush appears to have been briefed, him later deflecting when asked and saying that he can’t talk about classified stuff suggests that he was told something at least.
In 2020 Obama also alluded to not being able to talk about it on account of it being classified:
When one becomes president, they’re privy to pretty much everything. But all anyone really wants to know about are aliens and UFOs. Barack Obama was no exception.
On Monday’s “Late Show,” the former president of the United States told Stephen Colbert that he “certainly asked about” their existence.
“And?” the CBS host pressed.
“Can’t tell you,” the former president responded.
Colbert took that as a definitive “Yes.”
“Because if there was none you’d say there was none, right?” Colbert goaded his guest. “You just played your hand. I thought you were a poker player. You just 100% showed your river card.”
“Feel free to think that,” Obama replied.
“I will,” the late-night leader said.
Trump has also at times given some interesting comments:
Trump also suggested he knew more about the topic than he was saying publicly in an interview with his son Donald Trump Jr. Referring to the alleged UFO incident at Roswell, New Mexico in 1947, he said: "I won't talk to you about what I know about it, but it's very interesting."
It’s interesting, inconclusive, but interesting.