In Browning’s poem, the patriot only describes the changed situation without any detail of what actually led to this change. But the reference in the third stanza of the poem suggests that the patriot did everything that is good for people and for his country. But people probably misunderstood him and took him to be the culprit behind some unfortunate events.
 
The mythological reference in “Alack, it was I who leaped at the sun / To give it my loving friends to keep!” may suggest that his actions somehow caused the death of his close friends. Maybe he is talking about some battle that claimed the lives of his dear ones. Whatever the case may be, the patriot is confident that he doesn’t deserve the treatment he is receiving today. His tone is rather regretful and ironic —

Nought man could do, have I left undone:
And you see my harvest, what I reap