With Republicans holding a 54-46 advantage in the Senate, and several incumbents in tough races, Nevada represents their best chance of flipping a Democratic seat. As of last week, polls showed Heck with a narrow lead, even though Republican nominee Donald Trump trailed Democratic rival Hillary Clinton in the presidential race here. The publication of Trump’s lewd comments about women on Oct. 7 threatened to put him further behind and hurt his fellow Republicans. Over the weekend, Heck joined dozens of Republican candidates in rescinding his endorsement of Trump.

Democrats have a formidable voter-turnout operation in Nevada, thanks in part to an alliance with the union representing casino workers. On Tuesday morning last week, the headquarters of Culinary Union Local 226 roared with the voices of a hundred union members in red T-shirts, folding pro-Democrat flyers before hitting the streets. When early voting begins on Oct. 22, the union will commandeer casino buses to carry voters to the polls.

Since Labor Day, these workers have been doing politics full-time, with their pay covered by the union. (Labor contracts allow them to take a leave of absence from their casino jobs.) According to Yvanna Cancela, its political director, Local 226’s parent organization plans to spend about $3 million on the general election in Nevada this year.

Koch Funding

For its part, the Koch network aims to spend over $200 million nationwide on political activity between last year and this year, making it a force to rival the major parties. The Kochs generally side with Republicans, but decided earlier this year not to back Trump. That leaves the Senate as their top priority.

Since 2014, the network has boosted the size of its grassroots operations across the country by 50 percent, according to James Davis, a Freedom Partners spokesman. That gives it a unique means of communicating with voters about Reid’s successor, he said.

"All he does is launch divisive, blatantly false political attacks rather than debating the issues on the merits," Davis said. "That’s why we’re engaged."

Last week, Marcos Lopez, 22, roamed the west side of town with a Koch-issued iPad in his hands and a water pack strapped to his back. Lopez works for Americans for Prosperity, the biggest and oldest of the Kochs’ grassroots groups. The iPad tells him which doors to rap, and lets him upload notes on each visit in real time.

The iPad leads Lopez and a colleague to Frank, a retiree in his 80s who’s shuffling across the street in moccasins to pick up his mail. They ask him to take part in a "survey," meant to highlight Cortez Masto’s support for Obamacare to voters who dislike the president’s health-care law. The man needs little convincing.

"She’s with that Reid," the man says. "We’ve got to dump her!"