It may not be illegal, but could certainly be immoral.

Consider... If I pay for a politician to run for office and they get elected and then I write a bill that lowers my taxes for him to push through into law, and then I donate to all (or even just enough of) those in congress to vote for it and it gets passed that may not illegal (right now) but many (me included) would certainly consider it immoral.

For example... if that reduction in taxes collected was offset by firing hundreds of workers in, say, the Center for Disease Control, and then we are left unprepared for a serious and deadly viral disease outbreak and 100s of 1000s of citizens die as a result... yeah, that qualifies as immoral for me.