I was trying to figure out in my head how many Vice Presidents there have been and came up with 48. I knew FDR had at least 3 and Nixon 2 but beyond that I couldn't think of any other President with multiple VP's. Not that they served concurrently. FDR went with different VPs in three of his four election bids, hoping to consolidate the Democratic base. When Spiro Agnew was forced to resign in October, 1973, Nixon picked Gerald Ford to be his right-hand man. As it turns out, there were other Presidents who had multiple VPs and Presidents who didn't have VPs, but the number remained 48.
Thomas Jefferson got rid of Aaron Burr when he became a burden in 1804, opting for George Clinton in his second run for office. Clinton would also serve under Madison, but when he died in 1812, Madison picked Elbridge Gerry to fill his place in the next election. Clinton was first of seven VPs to die in office.
Andrew Jackson got rid of a toxic John C. Calhoun in 1828 and chose Martin Van Buren to be his running mate in the subsequent election, no doubt to rally New Yorkers and New Englanders behind him. Van Buren would subsequently win the office of the Presidency in 1836.
John Tyler was the first President to not have a Vice President. He chose to stay in office alone following the death of William Henry Harrison. The same was true for Millard Fillmore. Franklin Pierce chose not to name a second Vice President after William Rufus de Vane King died shortly into his term. I don't know the reasons for this. Maybe it was out of respect for their predecessors, or it was felt that the Vice President should not be an executive decision, but be ratified by the Convention. Later, Andrew Johnson would similarly not name a Vice-President after succeeding Lincoln into the White House.
It seems the only time a President replaced a Vice-President during his term was when Richard Nixon picked Gerald Ford to succeed the disgraced Spiro Agnew in 1973. It would turn out to be a fortuitous moment for Ford, who had previously been the Republican House Minority Leader. I vaguely remember the events that swirled around this appointment. House Speaker Carl Albert was actually next in line to the President when momentum began to build for Nixon's resignation. Surprisingly, Democrats helped confirm Ford by a resounding 92-3 margin in the Senate, with none other than Carl Albert swearing the new President in. That must have been a bitter pill.
Most of these Vice Presidents have long been forgotten. Oliver Stone tried to revive Henry Wallace from the dead, imagining a better world if Wallace had been Roosevelt's VP in 1945 and not Harry S. Truman.
This brings us to Mike Pence. He seems to have an unusual amount of authority on foreign matters. Trump is using Pence as a surrogate in meeting with foreign leaders abroad, given his numerous gaffes. Our current President prefers the comfort of Mar-a-Lago in entertaining foreign leaders, at least those he deems worthy of his "Winter White House." It has become kind of like the Tsar's Winter Palace. Trump obviously doesn't like anything more than a one or two-hour plane flight.
Our current president doesn't look in the best of health and now that the dust has settled from his bombing missions, the investigation into his administration's ties with Russia is once again edging into the news. This could mean we see VP Pence succeed Trump before 2020. Whether Pence would pick a VP or not depends largely on the outcome of the 2018 midterms. Should the Democrats stage an upset in the Congressional elections, Pence would have no other recourse than to nominate a no. 2 man to insure the White House stay in Republican hands if god forbid anything happened to him.
For now, Vice President Pence is content to wear the cuff links of no. 48.