(CNN) Billionaire philanthropist turned political activist Tom Steyer has already made a big investment in the 2018 election, but in the closing days of the campaign, Steyer has picked his favorite candidate and is pulling out all the stops.

Steyer is personally donating $2 million to Andrew Gillum's "Forward Florida" political action committee, which is aligned with the Gillum campaign. Through his organization, "Need to Impeach," he is directing a massive direct mail pitch to 300,000 Florida voters that have signed up to support his effort to impeach President Donald Trump. The mail piece makes specific reference to Gillum's support of impeachment.

Another organization funded by Steyer, NextGen America, has already spent more than $5 million on efforts to get Gillum elected.

"If you were going to choose a single race that has the most national significance, it would be the governor's race in Florida," Steyer said.

Gillum is running against former Republican Congressman Ron DeSantis and the race will be one of the closely watched contests in November since DeSantis has tied himself to President Donald Trump and defeated more establishment Republicans. Gillum, meanwhile, would become the state's first black governor, and has the backing of progressives like Bernie Sanders.

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