If you doubt the influence of the two major parties in America, ask yourself why all elected "progressive" leaders now endorse the very people they campaigned on opposing.
Recently, both Alexandria Ocasio-Cortez and Bernie Sanders endorsed Joe Biden. These endorsements not only come more than a year out from the next election, but they are for a candidate who is embroiled in a scandal as dire as anything of which Donald Trump or the Trump family has been accused. AOC endorsed Biden on the day he approved sending cluster bombs (deemed illegal by more than 100 countries because of the high rate of civilian deaths) to Ukraine. Bernie Sanders has called Biden his friend while Biden has exhibited racist tendencies and passed racist laws like the crime bill of 1994 which he wrote. Both Sanders and AOC have made the claim that Biden has done a good job as president, but failed to mention one thing he's done that has benefitted the majority in America.
If you want to know what Biden has done as president, watch the following video within this video at this link. https://youtu.be/YA1wfddkP4c