Alternate history

At the famous 1970 encounter between Elvis Presley and Richard Nixon at the White House, the "King of Rock and Roll" got his coveted Federal Narcotics Agent-at-Large badge, and "Tricky Dicky" received a gold-plated World War II commemorative Colt .45 in return.

This is the first part of a four-book alternative history set during World War II. Pearl Harbor was bombed, Panzers rolled through Paris--and then the real enemy lands.
Can the combined forces of all the Earth's armies stop the invading aliens?