Russian citizens are set to begin voting on constitutional changes that could allow President Vladimir Putin to remain in office for years to come, potentially cementing his hold on power and putting to rest speculation as to who might eventually succeed the Kremlin leader. If passed, the constitutional amendments would reset the clock on presidential term limits, allowing Mr. Putin to run for two more terms after his current tenure ends in 2024. Currently, term limits would compel Mr. Putin, who has held power in Russia…