I read Times magazine and found it difficult for me to figure out the exact meaning of "bums" in the following sentence.

" For many voters in the heartland, the Jack Abramoff congressional lobbying scandal has simply confirmed their suspicion that all the bums inside the nation's capital are on the take. "

I did try to look on several dictionaries but still not sure of the exact meaning of the word. Please kindly suggest.

"Bum" is a word with the broad meaning of a person you don't like, don't trust, won't do the right thing, isn't honorable, etc.

The guy my daughter is dating is a bum.

Congress is full of bums. We oughta' throw the bums out. (Although not grammatic, the way "kinda" isn't a word, there's an expression of "oughta throw the bums out" meaning we should not vote for this group anymore an elect new representatives.)
Hello Zenoline

Additionally, "bum" means "buttocks", in British English. So the sentence has quite a different (and somewhat disconcerting) meaning on this side of the Atlantic.