Mr Congressman, you have lost my vote forever. Furthermore, I will be campaigning on behalf of $OPPONENT who still believes in freedom and our greatest liberties. The fact that we have great men like $OPPONENT proves American democracy still works.
A response informing the congressman of why he's wrong, citing loss of jobs and liberty while threatening innovation, all in the name of an ever-growing government keen to erode our rights in the service of special interests, would likely hit enough republican talking points to at least merit a moment's consideration. Which, at the end of the day, is probably the best you could hope for.
Hit them where it hurts. Threaten _their_ job. If you lose your job due to their legislation, they'll just blame their opponent and tell you to stop begging for handouts.
In short, it's going too far, and even if it isn't, certainly seems like an idle threat.
Saying something more like "I cannot vote for any candidate who supports this policy or any like it" is perhaps a more effective statement to make.
"But it is necessary to know well how to disguise this characteristic, and to be a great pretender and dissembler; and men are so simple, and so subject to present necessities, that he who seeks to deceive will always find someone who will allow himself to be deceived. One recent example I cannot pass over in silence. Alexander VI did nothing else but deceive men, nor ever thought of doing otherwise, and he always found victims; for there never was a man who had greater power in asserting, or who with greater oaths would affirm a thing, yet would observe it less; nevertheless his deceits always succeeded according to his wishes, because he well understood this side of mankind.
"Therefore it is unnecessary for a prince to have all the good qualities I have enumerated, but it is very necessary to appear to have them."
http://www.constitution.org/mac/prince18.htm (As they say, read the whole thing... the chapter, anyhow.)
So your choice is either to concede that issue or vote for a fringe party (which here in the UK basically makes your vote worthless).
The same way the NAACP was embraced over the Black Panther Party.
See: https://en.wikipedia.org/wiki/Revolutionary_movement_for_Ind...