How did the US presidential campaign get to be so long?

While other countries set strict limits on the length of campaigns, American presidential races have become drawn-out, yearslong affairs. It wasn’t always this way.

Why Are U.S. Elections So Much Longer Than Other Countries'? : It's All Politics : NPR

What was the longest presidential election in US history?

How to make our election cycles shorter

Who is to blame for this awful US election?, US elections 2016

Why do U.S. elections cost so much?

Radio host Larry Elder ends Republican presidential campaign

Dirty Money: U.S. Presidential Elections 2016: Arunachalam, Mr Ramesh S: 9781537680095: : Books

Analysis: How Did The Presidential Campaign Get To Be So Long? - Government Executive

A History of U.S. Presidential Elections in Maps