If you want to understand why America is stuck with a broken two party system, look at France, which also has a presidential system but still manages to have multiple competing parties.
The first round of the French Presidential election will take place in a few days — April 22nd. Currently the polling for this first round is extremely close. Despite the fact that the incumbent, Nicolas Sarkozy, is deeply unpopular, he and Francois Hollande are neck and neck in polling for the first round, with several other candidates all polling in the low double digits. There is also Marine Le Pen, who is to the right of Sarkozy, and Jean-Luc Melenchon, who is to the left of Hollande.
A recent Opinion Way poll found Sarkozy at 28%, Hollande 27%, Le Pen 16%, Melenchon 13%, Francois Bayrou 10%. On the other hand, a recent TNS poll found Hollande 28%, Sarkozy 26%, Melenchon 16%, Le Pen 16%, Bayrou 9%.
Even though the vast majority of French don’t want Sarkozy to serve another term, there is no agreement on who should replace him. As a result this divided field means there is a real possibility Sarkozy could pull off a narrow plurality on April 22nd.
If France used the American election system for president this would mean a very unpopular incumbent could win another term. Afterwards there would be much finger pointing about how Melenchon was a “spoiler” that cost Hollande the election. There would have been real pressure on Melenchon not to run so the left could offer a united front in the election.
Under the French election rules though, if the unpopular Sarkozy wins a small first round plurality because of a divided field, that isn’t the end of the story. On May 6th the two candidates that did the best in the first round complete in a run-off election. The polls show that when the unpopular Sarkozy is faced with a single candidate, he should be easily crushed. Opinion Way has Hollande leading 54% to Sarkozy 46% in a possible match up. Similarly TNS has Hollande winning 56%-44%.
Because France uses a run off system, multiple parties can run candidates without the fear that a divided field will inherently favor even any unpopular incumbent. There’s less worry that simply having more parties running on one side of the political spectrum will inherently cost them the election.
France doesn’t have multiple viable political parties simply because the French people have greater diversity of views, any more than most Americans are simply super happy with just two parties. France has more parties because they have election laws that allow for a diversity of choices to have a chance of winning. In contrast, in America the Democrats and Republicans have worked together to write our election laws to try to prevent any other political parties from competing against them.