[Puck Luck]

so a few weeks ago, my wife caught a mouse in the pantry. Of all the things in there, the fury guy went after a Reese's peanut buttercup. She caught it with a cup and was able shoo him out the front door.

Last week, he or another mouse and a few friends came back. Again in the pantry but going for coffee crsip. I made a stop by Homedepot and got some live mouse traps. That night after setting up with coffee crisp as bait we caught 3 in the trap. This time we drove a few km's away and let them go in the park. We caught one more a couple nights later and i'm pretty sure we got the whole gang. (this gang anyway). Haven't seen any poop droppings since.

My question is how the heck they got in. I know they can get through the smallest hole or crack. I've searched all around the house along the foundation and up the walls but can't see how they could've got in. We have no trees, bush or tall grass up against the house.
I did notice that our front door has a gap under it as you can see in the pictures.
Could a mouse get under that small gap and have enough strength to push his was under the sweep? (i'v adjusted that sweep since so that it now actually sweeps)