There must be a legislation that once support letter is given, it cannot be withdrawn till next elections ( i.e., 5 years).
But such legislation can only be done by political parties, and we have to suffer because politicians are worst scoundrels, who will not pass such legislation.
Recall of MP/MLA s is another legislation required,but will not be done by selfish politicians. Once they win from some party, they should not change it in between elections. If they do so they(and their relatives) should not be allowed to contest again.
But will this happen in India ? I don't think in the near future it is possible. Solution is to punish one such politician., by public, in public, for the public-- like lynching. It may sound harsh, but perhaps necessary agst such politicians.