In addition to the delegates to the state convention of any political party as provided by section 595, all incumbent members of the state legislature shall be entitled to attend the convention of their political party as delegates at large of the county in which they maintain their legal residence. Such delegates shall not have alternates. He may attend the convention of the county, counties, or portions of counties which he represents in the state legislature and may choose to vote in any or all said county or district caucuses, but having only 1 vote on the floor at the state convention.