President Vladimir Putin has signed a law granting former Russian presidents expanded immunity from prosecution and allowing them to become senators for life in the upper house of Parliament once they leave the Kremlin. The new law follows sweeping reforms of Russia’s political system initiated by Putin this year. Among other things, it allows him to run for two more six-year terms in the Kremlin if he chooses. The legislation was part of constitutional amendments that were approved this summer in a nationwide vote that allowed Putin to remain president until...