Brutus was a man of principle who loved his country and was willing to risk everything of personal value, including his own life, to preserve freedom for his countrymen. However, he was naive, and he was a terrible judge of character. Cassius manipulated him into the conspiracy, and Antony manipulated Brutus into allowing him to speak at Caesar's funeral. Antony then manipulated the crowd to run Brutus out of Rome. Brutus understood honor, but he didn't understand power and those who prized it above all else. Brutus would not have fared any better today than he did then. He was ill equipped for political in-fighting.
Cassius was clever, devious, ambitious, and persuasive. He might be able to work his way into a position of political leadership today, but he would overreach himself eventually. People would not follow him as a leader for very long because he lacked ideals and principles; he had nowhere to take them. His vision extended no further than self-promotion. Other politicians like Cassius would recognize him for what he was; if he became too powerful, one of them would beat him at his own game since Cassius frequently ignored his own intuition and political instincts.
Brutus is the noble but naive one who goes to Washington with stars in his eyes and a will to do the right thing. However, he is manipulated into doing the "right thing" for others which is the "wrong thing" for himself. This is a common story in politics. Eventually, his conscience would bother him and he would quit, or he would stop listening to his conscience and live this way for a long time, getting re-elected all along.
Cassius is the wily one who doesn't mind using all the tricks in his book to get what he wants. He would do well in Washington politics or even somewhere known for its dirty politics like Chicago or Louisiana. He does the dirty work but manages to stay clean-looking. He may even be backed by crooked groups who stay out of the picture, but keep his dirty politics afloat with lots of funding. There are skads of politicians who fit this bill. Some of them have even made it to President in their lifetime. Cassius would do well.
They both wouldn't fare too well. To succeed,you need good judgement or at least a "stick to your principles" type personality. They had neither.