Since 1950, the January primary front-runner, according to national polling, has been more likely to lose the primary than to win it. 
Andrew Yang is in 5th place in some DNC qualifying polls, and is getting between 3-6% among those polled.
In the 1st half of 1975, Jimmy Carter was in 16th place out of 18 candidates. He polled at 0.8%.
In the 2nd half of 1975, Jimmy Carter moved up to 13th place, out of 13 remaining candidates. His polling number had actually dropped to 0.5%.
In 1976, Jimmy Carter won the primary with 40% of the vote.  He went on to win the Presidency.
In the 1st half of 1991, Bill Clinton was tied for 11th place out of 18 candidates. He polled at 1.3%.
In the 2nd half of 1991, Bill Clinton’s polling improved to 7.4%, putting him in 4th place.
In 1992, Bill Clinton won the primary. He went on to win the Presidency.
In December 2003, John Kerry was in 6th place. He polled at 4%.
In 2004, John Kerry won the primary.
In July 2015, Donald Trump was in 7th place in the Republican primaries, polling at 6.5%.
In one week, Trump leapt into 1st place.