WASHINGTON — Russia has continued its support for President Donald Trump by actively trying to undermine the candidacy of Joe Biden, the presumptive Democratic nominee, according to a U.S. intelligence assessment released Friday that suggested wide-ranging foreign threats to the November election. It was a striking warning from Trump’s own top intelligence officials, further eroding his repeated attempts to downplay or deny Moscow’s well-documented help for his campaign in the last election. It also suggests that an effort by Republicans in Congress to investigate Biden for his previous work in Ukraine could become a vehicle for Russian disinformation. The unclassified “election threat update” said Russia is using a “range of measures” to denigrate Biden, whom the Kremlin blames for supporting pro-democracy groups opposed to Russian President Vladimir Putin while Biden served as President Barack Obama’s vice president. The statement stops short of accusing Russia of directly working to elect Trump, but notes that some “Kremlin-linked actors” are seeking to boost Trump’s reelection campaign on social media and Russian television. Two other American adversaries are also trying to influence U.S.