Americans for Prosperity, the heart of the billionaire Koch Brothers’ conservative political network, plans to ramp up its campaign against Ralph Northam, the Democrat in Virginia’s governor’s race.

The conservative group announced Friday that it would spend at least $1 million on mailers and digital ads targeting Northam’s record on taxes, education and economic development.

It follows at least $1.8 million in anti-Northam television commercials and mailers to date, according to data collected by the nonpartisan Virginia Public Access Project. The group also says it has contacted hundreds of thousands of Virginia voters through its phone-banking and canvassing efforts.

Northam faces Republican Ed Gillespie in three weeks. Their race, the nation’s only competitive statewide contest this year, has drawn millions in spending from outside groups.

Americans for Prosperity's advertising does not explicitly tell voters to support Gillespie, but its anti-Northam spending helps the Republican contender make up for a financial disadvantage. Northam had more than twice as much cash in campaign accounts than Gillespie heading into October, records show.

Democratic candidate for governor, Lt. Gov. Ralph Northam, left, shakes hands with Republican challenger Ed Gillespie after a debate at the University of Virginia-Wise in Wise, Va., Monday, Oct. 9, 2017. (Steve Helber/AP)

The latest push includes a mailer that blasts Northam for supporting an increase in taxes on sales, gasoline and home and car purchases.

It refers to sweeping 2013 legislation to raise revenue for transportation and road projects that was supported by then Republican Gov. Robert McDonnell and passed the General Assembly with bipartisan support.

Gillespie has softened his criticism of Northam for supporting the transportation deal, which was also supported by business groups that lean Republican, and has pledged not to repeal the legislation.

Americans for Prosperity is also launching a digital video featuring a charter school administrator criticizing Northam for voting against a bill to establish "educational savings accounts" that allow parents who remove children from public schools to receive 90 percent of the state funding that would have been spent on their child. They would be able to use the funds for private-school tuition, tutoring, books and other educational costs. Critics say such accounts are similar to vouchers in that they drain resources from public schools.

Gillespie supports educational savings accounts; Northam is opposed.

“We’re confident that this renewed effort over the coming weeks will help us share Northam’s record to Virginians, and they won’t like what they hear,” Americans for Prosperity Virginia director J.C. Hernandez said in a statement. “From backing tax hikes to the bad deals with taxpayer dollars, Northam’s fiscal policies would make life more expensive for households across the state.”

The latest stories and details on the 2017 Virginia general election and race for governor.

Americans for Prosperity is the largest outside group aiding Gillespie's candidacy. The National Rifle Association is spending at least $760,000 on pro-Gillespie commercials, according to records compiled by the Virginia Public Access Project.

Meanwhile, Northam has a constellation of progressive groups canvassing and overseeing digital advertising program on his behalf. They include billionaire environmentalist Tom Steyer’s NextGen America, as well as the political arms of Planned Parenthood and the Virginia League of Conservation Voters.