Is the US closer to the sun during the winter or the summer?

Neither. The United States (assuming that's what you meant), is a territory of land on the surface of the planet earth and thus does not move in respect to the rest of the planet.

If your question was: "Is the planet earth closer to the sun during the winter or the summer of the northern hemisphere?" Then the answer would be that the planet earth is slightly closer (by 0.033 AU or ~ 5 million km) to the sun during the winter solstice than the summer solstice.