Section 28. Justices and judges of courts of record shall not be eligible for any other public office or for any other public employment during their term of office, except that they may assume another judicial office, and upon qualifying therefor, the office formerly held shall become vacant. No justice or judge of any court of record shall practice law during his continuance in office, nor shall he hold any office in a political party or actively take part in any political campaign other than his own for his reelection or retention in office. Any justice or judge who files nomination papers for an elective office, other than for judge of the superior court or a court of record inferior to the superior court in a county having a population of less than two hundred fifty thousand persons according to the most recent United States census, forfeits his judicial office.