The Pooch and the Pauper.

The bulldog Liberty (who's thoughts we're able to hear) is the "First Dog of the USA", i.e. the president's dog. As such he has a lot of representative duties, but also many privileges which made him snobby and condescending towards other dogs. But one day when the young Nataniel takes him for a walk, he's mixed up with the stray dog Moocher who looks like his identical twin. Henceforth Moocher takes Liberty's place in the White House. From now on a different spirit reigns in the White House