A lot of people are saying that the fear comes from lobbyists and the interest groups they represent giving money to opponents. That is partially true, but money is just part of the overall influence that the interest groups lobbyists represent wield.
In the case of ReadyReturn, one of the key players is Grover Norquist, an anti-tax activist. (see https://priceonomics.com/the-stanford-professor-who-fought-t... for some of the older history here) He has this incredible network of anti-tax groups, media figures, and others that can be activated to attack and take down politicians, particularly republicans, without spending a dime (altough they also have money to spend).
It might seem wrong, but it is fundamentally the same mechanism by which liberal action networks (like human rights campaign or NARAL) drive their political influence as well.
It is these networks of influence that politicians really fear, because they are so much more effective then money.
In the case of ReadyReturn, one of the key players is Grover Norquist, an anti-tax activist. (see https://priceonomics.com/the-stanford-professor-who-fought-t... for some of the older history here) He has this incredible network of anti-tax groups, media figures, and others that can be activated to attack and take down politicians, particularly republicans, without spending a dime (altough they also have money to spend).
It might seem wrong, but it is fundamentally the same mechanism by which liberal action networks (like human rights campaign or NARAL) drive their political influence as well.
It is these networks of influence that politicians really fear, because they are so much more effective then money.