If the US government really had alien bodies, then the US president would know about it.

If the US president knew about it, then Trump would know about it.

If Trump knew about it, he would have told everyone, bragged about it, kept boxes of documents about it at Mar-A-Lago, etc. There would be a ketchup stained original photograph of an alien autopsy on the floor of his bathroom.

Since we haven't heard him brag about having seen a photo of an alien, we know that he hasn't seen one.

#aliens

Trump says he's heard 'very interesting' things about Roswell, site of an alleged UFO event

President Donald Trump says he’s heard some interesting things about Roswell, where a UFO event happened, but he’s not sharing even with his eldest child.

NBC News