Pretty much anything they want
I'll give you GATE as an example. Portal to a fantasy world opens up in the middle of Tokyo and while a lot of havoc is caused immediately and hundreds of people are killed, the moment the Japanese military mobilizes and gets boots on the ground, they set up a defensive perimeter on the fantasy side in about a day. The nearby kingdom eventually sends its army over to attack what it sees as an invasion and gets thoroughly slaughtered because they sent swordsman and cavalry against machine gun emplacements. The JDF probably had only a hundred or so men manning their encampment and the kingdom's army was measured in thousands (the JDF saw no losses, as not a single man from the massive army made it within 400 feet).
The JDF eventually has an encounter with a dragon and while it shrugs off a lot of the munitions thrown at it, they eventually blew off one of its forelegs with a portable rocket launcher (then tracked it down to its lair, set up C4 charges, and blew it up). Oh, and the team that was dealing with this problem? Four. 160
It took just four guys (in a jeep) to defeat a dragon that was shrugging off anti-vehicular machine gun rounds.
Humans to aliens with interstellar capabilities are going to go down much the same way. "Why don't we drop a nuke on them?" well, because insert technobabble here and their whatever tech stops it. Maybe the aliens have energy shields, maybe they can detect nuclear warheads hundreds of miles out and shoot down the bomber, maybe they've got some kind of containment device. Whatever fits your bill.
The aliens being tired from a long journey is almost irrelevant when they can field one man for every ten thousand of humanity and still call it a fair fight. Especially when they can land, set up base, and not even really be noticed by the local authorities for a couple days. Even then they'd just have to deal with the hundred or so local police and then have a week before anything significant (the military) shows up. 160