WASHINGTON — A new report by congressional Democrats warns of deepening Russian interference throughout Europe and concludes that even as some Western democracies have responded with aggressive countermeasures, President Donald Trump has offered no strategic plan to bolster their efforts or safeguard the U.S. from again falling victim to the Kremlin’s systematic meddling. The report is the first from Congress to comprehensively detail Russian efforts to undermine democracies since the 2016 presidential election.