In 1824, Andrew Jackson lost the election in the electoral college to John Quincy Adams after winning the popular vote. Jackson rallied his backers and won four years later.
In 1888, Grover Cleveland won the popular vote but lost the electoral college to Benjamin Harrison. Cleveland ran again four years later, and won.
In 2000, Gore won the popular vote but lost in the electoral college to George W. Bush. Gore apparently let it get to him, put on a lot of weight and had his marriage fall apart.
If Gore truly felt he was robbed, he could have run again. Nobody was stopping him. I don’t have any sympathy with whiners.
1n 1960 Nixon lost the race to JFK by one of the closest margins ever. Refusing a recount as being divisive, he came back to win the Presidency in 1968.
Add, in 1976 Reagan lost and was beaten down by the RNC establishment. He came back in 1980 and 1984 to two landslide victories in a row.