Top U.S. intelligence and homeland security officials are raising alarms about potential efforts by Russia to influence the 2018 and 2020 elections.

National Security Adviser John Bolton says President Trump has directed a "vast, government-wide effort" to protect American elections after Russian attempts to interfere in 2016.

In a letter to Senate Democrats Thursday, he says: "President Trump has not and will not tolerate interference in America's system of representative government."

Homeland security chief Kirstjen Nielsen says: "Our democracy is in the crosshairs."

Bolton's letter comes weeks after Trump publicly undermined the conclusions of American intelligence agencies regarding Russian interference. After suffering a bipartisan outcry, Trump later said he accepted those conclusions.

Bolton now says Trump is "leading unprecedented action to punish Russia" for its efforts to disrupt American elections.

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