I heartily agree with the remark that no man who has unsparingly thrown himself into politics, trusting in the loyalty of the democracy, has ever met with a happy death.

You can count me +1 on that. The quote comes from Pausanias, in reference to Demosthenes. Demosthenes had a negative experience when he advised the Athenians to fight Philip of Macedon and his son, a lad by the name of Alexander, and after Alexander died one of his successors called Antipater. After the Athenians had been totally crushed by Antipater, they decided to hand over their leaders for retribution, in the hope Antipater wouldn't raze Athens to the ground and enslave the entire population (no idle concern...Thebes was previously destroyed by Alexander for much the same behaviour). Demosthenes took poison to avoid an inevitable ugly death.

But Demosthenes wasn't the only Athenian leader to suffer. Ancient Athens had a long history of ultimately destroying their best men.

Miltiades, who led them to victory at Marathon, was a year later unjustly convicted of taking bribes from the Persians. He would have been sentenced to death, but in consideration of him winning the most important battle in human history, the sentence was commuted to a fine of a "mere" 50 talents, which he couldn't pay, so he died of war wounds while languishing in prison. His son Cimon was still required to pay the fine. The prosecutor was Xanthippus, the father of Pericles.

Cimon himself proved a fine military commander and an outstanding benefactor of Athens (he built the Academy out of his own pocket). So naturally he was ostracized. The prosecutor was Pericles, son of Xanthippus. (You might be spotting a trend here...) Cimon too died of war wounds while in exile.

In an interesting example of karma at work, Pericles himself when an old man was prosecuted and fined 50 talents. The charge was theft from the public purse, but his real crime was leading the Athenians into a war against Sparta, which didn't work out as planned. Like Miltiades and Cimon, he was almost certainly innocent. He died shortly after of the Great Plague.

Socrates, as is well known, was pretty much judicially murdered. So too was Pericles, the son of Pericles and Aspasia, along with other generals, after they won a sea battle, but didn't win it well enough for the liking of the populace.

Themistocles, the strategic genius who led Athens and all of Greece to victory against Persia in the face of almost impossible odds, was the only one to be brought down and survive. He was ostracized because people feared he was so powerful he might make himself tyrant of Athens, and while he was in exile he was convicted in absentia of treason on trumped up charges on the basis of falsified evidence supplied by Sparta. Themistocles broke the trend though on unhappy deaths. He was smart enough to run while the running was good. He went straight to the court of the Great King of Persia, where he was honored and made a minor satrap and lived in sumptuous luxury. He was quoted as toasting a dinner with the words, "I would have been undone, had I not been undone."