and what? Threaten to put somebody in jail for life? :)
Put them in jail but keep the politician in office, yeah. That ruins the blackmail.
Not in general. A party/community will use code words to indicate that they're threatening.
It happens right now and it would happen even more when there is a 100% chance of success.
So suppose a certain group calls themselves zeta.
They have about a hundred thousand members spread relatively evenly throughout the country. They can't win any elections, but they have a very high 'radicalization' quotient, that is most of them are convinced that they are being brutally oppressed and 10% of them are willing to go to prison to change things. If assassination would change things instead of turning the public against them, they would certainly assassinate.
If you think such a group is unrealistic, I beg to differ, I think there are 20 such groups right now.
That's 10,000 vetos in their arsenal, and they have no way to win elections.
They don't need to convince the public or a party or even the candidate lineup. All they need to do is convince the current leader that someone in their group will take them out.
So they will use weasel words, dog whistles, and coded language.
"If you don't, people will not stand for it" (wink wink nudge nudge)
"This is intolerable, it's worse than life in prison" (wink wink nudge nudge)
You can't throw anybody who uses such language in prison, and even if you did; that means they can use that power to protect a candidate. Want someone to be immune from "assassination"? Just threaten to "assassinate" them.
You think you can lineup 10,000 candidates and not one would give in? That is absurd. The only reason they might not give in would be because they know if they did, somebody else would "assassinate" them because you can't make everybody happy (so long as somebody is irrational).
Then it's not a game between the candidate and the public, it's a game between the groups that hate each other's policies, a game of sacrifice, and we know what that game looks like: it's called war.
Politics is war by other means and this is form of war that gives the advantage to those most convinced that they're right, not the unselfish.