Option B
You investigate further, and try to find a specific vote that has been effected by the Senator’s problem.
If you had printed the story you probably would have been sued for libel. Stating that the Senator has a problem with alcohol is a defamatory statement. The Senator as a public official has to prove actual malice, which he could have, if you could not produce a specific instance in which his ability to vote was impaired. The evidence that the Senator does drink before returning to the Senate would help your case, but it would not get you off the hook completely.
OR