MOSCOW (AP) — The 15-day jail sentence imposed Monday on Alexei Navalny is nothing new for the Kremlin's most visible domestic foe, and is unlikely to be more than a brief interruption of his campaign against what he calls "the party of crooks and thieves." Amid all the detentions, the 40-year-old Navalny has relentlessly pursued corruption investigations that allege the top tier of Russian officials, including Prime Minister Dmitry Medvedev, have amassed extraordinary wealth, living lives of unparalleled luxury behind their modest public images. FIRST PROTEST WAVE The size and persistence of the protests — which were held sporadically for months —appeared to take the Kremlin off guard after years of regarding opposition groups as irrelevant, if annoying, minorities. The crackdown appeared to sap the opposition's momentum and the Kremlin cemented its advantage by sharply increasing penalties for participating in unauthorized demonstrations — up to five years in prison for a third violation.