What is the main issue of campaigns for third party candidates in us elections?

In the middle of bipartisan domination, the votes obtained by third party candidates can unbalance the general one. The US electoral system is designed by and for bipartisanship. Even the third party percentage of voters is generally lower than republicans and democrats, it has been used as an opinion stroke in order to decide the presidential fate in several states of US.

Third party candidates can be spoilsport for Democratic or Republican candidates.

Some Bush campaign officials believed that Perot spoiled Bush's reelection.

the section of the chart that represents a point at which a bill needs approval from a majority of people in both chambers to advance is j, as this is the only section before the bill becomes law which has both rows (symbolizing the chambers) converging into one, meaning that the two parts of the congress have to approve of it before it can march on with the process.