The big picture: There have been five other cases since 1950 when seats have opened within 150 days of a midterm election. In three of them, the nomination process was completed before the election (David Souter, Antonin Scalia, Arthur Goldberg). In the remaining two instances, both under President Eisenhower, the nomination was delayed until after the election (Potter Stewart, John Marshall Harlan II).
Why it matters: Mitch McConnell, who stalled Merrick Garland’s nomination to replace Antonin Scalia because it was close to a presidential election, has promised that Kavanaugh's confirmation hearings and vote will take place before November.
The bottom line: Democrats are looking for ways to block or delay the nomination, but they don't have the votes to do it as long Republicans stick together.