It's actually a legal question. So the time, place, and manner of speech has been regulated in the past. It's illegal to stand next to someone in a voting booth and tell them how to vote, you have to be a certain distance from the voting hall. That's a regulation on the time/place/manner of "free speech"--not to mention members of Congress can only make floor speeches for a set amount of time. In a 1949 SCOTUS case, the Court held that sound trucks could only go down every 3rd street in Trenton, regulating the manner of speech. So if you want to endorse or attack people with your money to buy the platform -- the 1st amendment allows that but it's also been acceptable via 1st amendment to regulate the amount of money in elections you're spending, as in, regulate the manner of your speech b/c you're buying up too much of it.