Colorado is one of a handful of states where Americans for Prosperity, the political advocacy group backed by the Koch brothers, will put money directly behind candidates in the 2018 election, state executive director Jesse Mallory told Colorado Politics Wednesday.

The powerhouse conservative organization plans to invest big in the three Republicans: Walker Stapleton in the governor’s race, incumbent Sen. Tim Neville of Littleton in Senate District 16 and Christine Jensen of Arvada in Senate District 20.

There is no set budget yet for the three campaigns, Mallory said.

It’s the first time ever that AFP is spending directly for Colorado candidates.

Americans for Prosperity is reviled on the political left for its ties to David and Charles Koch, the billionaire Wichita-based businessmen. The organization historically shapes policy and organizes grassroots efforts that are favorable to Republicans.

Colorado Politics’s Marianne Goodland reported last week that the Koch-funded AFP had created a campaign committee in Colorado.

The Colorado Sun news website reported Wednesday that AFP’s spending on the Stapleton race could reach nearly $1 million, but Mallory said that figure is speculative. The organization has made an initial low six-figure investment in Colorado TV ads, mailers and other work to elect the three candidates, he said.

AFP will adjust that budget upward without a pre-determined cap based on the closeness of the races as the November election nears, Mallory said.

Despite recent reports that the Kochs’ political operation might back some Democrats in the 2018 election, it was never a close decision on whether to support Republican Stapleton or Democratic nominee Jared Polis. AFP previously had said it intended to endorse Stapleton.

“A lot of it has to do with Walker’s positions on TABOR (the Taxpayer’s Bill of Rights), controlled spending and holding down debt,” Mallory said. “We think he’s a champion on those issues that we hold dear.”

He said the same of Neville, who is facing Tammy Story in November, and Christine Jensen, who is running for an open Senate seat against state Rep. Jessie Danielson.

Those two seats, along with Rep. Faith Winter’s run against incumbent Sen. Beth Martinez Humenik in Senate District 24, likely hold the key to power in the legislature’s upper chamber. Republicans have a one-seat majority, while Democrats enjoy a seven-seat edge in the 65-member House.

If Polis wins the governor’s race and Democrats keep the House, Republicans view the Senate as a firebreak against an unimpeded liberal agenda in the statehouse.

In response to AFP’s support for Stapleton, Polis’ spokeswoman, Mara Sheldon, said: “Walker Stapleton is bought and paid for by out-of-state special interests. He’s marched in lockstep with the Koch brothers’ agenda of robbing Coloradans of their health care and decimating our public schools. Jared Polis is the only candidate in this race who will fight for Colorado families.”

The Stapleton campaign turned the issue toward Polis’ refusal – similar to Stapleton’s so far – to release his recent tax returns.

. RELATED: Polis fires back at GOP attack over income taxes, calls on Stapleton to release tax records

“Congressman Polis has spent nearly $20 million trying to buy this election and has not even answered for how his wealth nearly doubled, to over $300 million, while he has been in Congress,” Stapleton spokesman Jerrod Dobkin said. “King Jared’s arrogance knows no bounds. He thinks he should be able to play by a different set of rules.”

Polis, a tech millionaire, has put in about $18 million of his own money in the race. Stapleton has reached in his own pocket for about $1.2 million.

Stapleton took heat in the primary from another self-funder, Douglas County businessman Victor Mitchell, who finished second in the primary.

“There are certain party establishment people that love Walker Stapleton,” Mitchell said in a Colorado Public Television debate in June, “because basically they can give him a tremendous amount of special interest money and they feel he’s more predictable, they can control him better.”

Stapleton did not participate in the debate.