The decision comes after recent polling put the candidates close. A survey conducted for Munson’s campaign by Workbench Strategy found Mazzei ahead 49% to 45% among 600 likely voters surveyed Oct. 8–13, before respondents heard messages about either candidate. The four-point gap was at the edge of the poll’s margin of error.

The poll was commissioned by Munson’s campaign, so its results should be viewed in that context. It also found that half of the surveyed Republicans who voted for state Attorney General Gentner Drummond in the GOP runoff said they planned to support Munson. That subgroup included only 72 respondents, making the finding less reliable than the overall results.

The DGA says its money will help Munson reach voters through television and digital advertising. The group’s spokesperson, Kevin Donahoe, described her campaign as grassroots-driven and focused on issues important to Oklahomans, and said the association believes she is in a strong position to win.

Mazzei, a former state senator and budget director under Gov. Kevin Stitt, won the Republican runoff against Drummond by roughly 2,000 votes. President Donald Trump endorsed Mazzei and campaigned for him after attacking Drummond, who had sued to block construction of a planned aluminum smelter, citing environmental, agricultural and foreign-ownership concerns.

Trump has promoted the smelter as part of his effort to expand U.S. manufacturing. His involvement in the primary has become a point of debate in the general-election contest, as some Republicans worry that the bruising runoff could leave party voters divided. Republicans familiar with the race have also raised concerns that Mazzei’s ties to state government and Trump could limit his appeal, though those sources say they still expect him to win.

Mazzei campaign spokesperson Jahan Wilcox rejected the idea that a Democrat could prevail, calling Munson a liberal and saying speculation about the race’s outcome came from people who do not understand Oklahoma. A spokesperson for the Republican Governors Association said Mazzei would lower taxes and protect families.

The Democratic investment is part of a broader effort by the DGA to compete in more states. The association recently announced a $10 million push in gubernatorial races it considers toss-ups, including contests in Georgia, Iowa, Nevada and Ohio. Oklahoma remains a steep challenge for Democrats: Trump won the state by 34 points in 2024, and the last Democratic gubernatorial victory there came two decades ago.