Washington (CNN) President Donald Trump and his allies have spent more than $33 million on Facebook and Google ads in the last year and a half -- more than four times his television spending -- as his aides race to build massive lists of supporters and donors ahead of the 2020 general election.

The onslaught by the President's campaign and the Trump Make America Great Again Committee -- a joint fundraising operation between his re-election effort and the national Republican Party -- exceeds what the top four Democratic candidates combined have spent on those platforms so far, and underscores his digital dominance a year before Election Day.

The Trump spending spree has set off alarms among Democratic strategists. This week, liberal political action committee PACRONYM announced a $75 million digital campaign to counter the Trump campaign.

"Last minute multi-million-dollar ad buys won't be enough any longer," David Plouffe, who managed President Barack Obama's 2008 campaign and serves on Acronym's board, said in a statement. "This election is already being fought and it's being fought online. There will be no magic message, ad, or candidate. We are going to have to grind out this victory the hard way, and it will take time to learn how to build the most effective case to the right voters. This is a DEFCON 1 situation."

The group's initial spending will focus on key battleground states, including Arizona, Wisconsin, Michigan, Pennsylvania, and North Carolina.

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