I don't believe it was "inadvertently". He knew it was illegal, and did it anyway. That's what he said in his guilty plea.
In May 2014, D'Souza pleaded guilty to one felony count of making illegal contributions in the names of others. D'Souza told Judge Berman, "I knew that causing a campaign contribution to be made in the name of another was wrong and something the law forbids. I deeply regret my conduct."
Hes lost the right to vote forever.
Depends on the State. The trend is to restore felon voting rights in many places. Terry McCauliffe wanted to do it for 400,000 in Virgina alone.
"Feingold and McCain cosponsored the Bipartisan Campaign Reform Act (McCainFeingold Act), a major piece of campaign finance reform legislation."