With the first national party convention just three weeks away, Barack Obama and John McCain still have not announced their running mate selections. However, both candidates have about two more weeks before their announcements will become the latest in recent comparable elections. In the last two presidential elections where neither candidate was a sitting president, three of the four nominees had made their picks by the end of the first week in August.

In 1988, Vice President George H.W. Bush and Massachusetts Gov. Michael Dukakis made their selections more than a month apart. Bush announced August 16 that he would be running with "a young man born in the middle of this century and from the middle of this country" -- Indiana Sen. Dan Quayle. Dukakis announced his pick of Texas Sen. Lloyd Bentsen more than a month earlier on July 13. Bentsen did not help Dukakis carry Texas, as the Democratic nominee had hoped, and Bush went on to win 40 states and 54 percent of the popular vote.

In 2000, Texas Gov. George W. Bush made the first move, announcing July 25 that Dick Cheney, his father's Defense secretary, would be his running mate. "I believe you are looking at the next Vice President of the United States," Bush correctly predicted that day. Vice President Al Gore waited two more weeks before selecting Connecticut Sen. Joe Lieberman on August 7. Bush won the election, of course, carrying 30 states, including Florida's disputed electoral votes, while Gore won the popular vote by about 550,000.