WASHINGTON — The chairman of the Senate Judiciary Committee wants his panel to vote as soon as next week on a bipartisan bill to prevent the undue firing of special counsels like Robert Mueller, according to aides familiar with his plans.Sen. Charles Grassley, R-Iowa, has asked for ranking member Dianne Feinstein's sign-off to make a last-minute addition of the bill to the committee's Thursday agenda, a move that would set up an April 19 vote on the legislation.