1.George Washington, Thomas Jefferson, Andrew Jackson, James K. Polk (covering the Mexican War like Henry VI part 1 covered the Hundred Years War and Henry V covered the victory at Agincourt), Abraham Lincoln, Ulysses S. Grant, Theodore Roosevelt, Woodrow Wilson, Calvin Coolidge, Herbert Hoover (Tragedy, perhaps?), FDR, Harry S. Truman, Dwight D. Eisenhower, John F. Kennedy, Richard Nixon, Ronald Reagan, George W. Bush, Bill Clinton, Barack Obama, Donald Trump. I know his plays mainly spanned the Plantagenet era, so he might focus on certain Preidents from a particular period in US history?
2.Would William Howard Taft be a comic figure? Will Rogers? Huey Long and William Jennings Bryan would make interesting characters.
3.Off-topic, but Shakespeare is said to have had an hand in the play "Sir Thomas More," and since there were several of that genre, a few plays about prominent congressmen, governors, or mayors might exist.