ARVADA — Perhaps the most consequential campaign in Colorado this fall is not at the top of the ballot.

A political linchpin in the Nov. 8 election is a state Senate district outside Denver, where 108,000 voters are expected to determine control of the Senate and Colorado’s policy direction for the next two years.

Laura Woods knows the stakes. If Republicans keep this seat — wrestled from the Democrats by 663 votes two years ago — the party will likely hold its one-vote advantage in the Senate. It’s the GOP’s only foothold in the Capitol.

But if Democrats unseat Woods with challenger Rachel Zenzinger, the party can claim complete control of the lawmaking process, with Gov. John Hickenlooper in office through 2018.

In Senate District 19, “the mood is similar to what’s happening all over the country,” Woods said as she walked between homes in Arvada on recent morning. “Everyone is wondering what’s going to happen. It’s the great unknown.”

The presidential race and U.S. Senate contest are less competitive in Colorado at this point than many pundits had expected, but the battle for control of the General Assembly is as heated as ever. A handful of House and Senate races are receiving national attention as a flood of money inundates voters with mailers and television commercials full of oddball attacks and, at times, outright lies. The Senate District 19 race is expected to top $1 million in spending.

“It’s such a strange year,” said Jeff Bridges, a Democratic state House candidate in a hyper-competitive Denver suburban district, giving a nod to Republican presidential candidate Donald Trump. “And I really think it comes from the top of the ticket — it’s as if they’ll say anything at all, regardless of whether it’s true, and it doesn’t really matter.”

Candidates and outside groups that are spending millions of dollars on state legislative races are, fairly or not, tying Republicans in tight races to Trump and Democrats to Amendment 69, the ballot measure that would create a state-run health care system. Also dominating the cross-charges from both sides are tax-and-spend issues, gun laws, abortion rights, and fracking and other issues that affect business interests.

Then, there are ever-present debates over the best ways to expand job training, strengthen the state’s economy, improve education and fix the state’s roads and bridges.

Amid the noise, each party knows the math. To win back the Senate — held 18-17 by the GOP — Democrats must keep two competitive open seats that Republicans are vying to win, and then flip at least one GOP seat — most likely Woods’.

In the House — now controlled 34-31 by Democrats — Republicans face the more difficult task of winning two Democratic seats for the majority while also beating back challenges to a few of its own endangered incumbents. (Read about six of the top races in both chambers.)

John Straayer, a Colorado State University political science professor who watches the state legislature, said the Senate is the focus, a point acknowledged by Colorado GOP chairman Steve House.

“I’d be amazed if the House went Republican,” Straayer said. “I think there are more at-risk seats on the Republican side.”

It’s hard to underestimate the stakes in the battle for the statehouse. The 2014 election installed a split legislature with a Democrat-led House and a Republican-controlled Senate, resulting in recurring gridlock. The balance required widespread approval for major initiatives even as the partisan divide encouraged lawmakers in both parties to push ideological legislation with no chance of passage.

If Republicans retain the Senate with a Democratic House, expect more of the same. Republicans are expected to put forward legislation that reduces state spending on Medicaid, the health insurance program for the poor; seeks to create a voucher program for private schools; and increases spending on road construction, possibly with new bonds.

Much of it will not win Democratic approval, but the party still can help frame the conversation at the statehouse.

“We certainly look to fight for regulatory common sense when it comes to the business climate here in Colorado, and that includes many things — industries across the board, including energy,” said Sen. Kevin Grantham, a Cañon City lawmaker likely to lead the chamber if the Republicans retain the majority. “And we want to keep a good check and balance on those things.”

If Democrats win the Senate and the House, expect the ruling party to approve an overhaul of the hospital provider fee to allow more state spending on education and transportation; a repeal of the death penalty; and a requirement for employers to give women equal pay.

“There are a lot of individual bills … that have historically not been able to pass,” said Senate Democratic leader Lucía Guzmán, who named the death penalty repeal as a priority. “We believe in putting the movement toward more renewable energy and bringing climate change and those issues to the forefront. And I think we can better do that under Democratic leadership.”

Still, Guzmán cautioned that Democrats learned their lesson after pushing a strong liberal agenda when the party controlled the statehouse after 2012, only to lose recalls and then Senate control in the 2014 election.

If Democrats win the Senate, she wants to see more moderation. “I think that good leadership could bring about an opportunity to bring us together — move us both, the Republicans and Democrats, to a new middle ground,” she said.

Republicans are less convinced. Even as they acknowledge Democrats are likely to keep the House, the GOP is fighting to narrow the margin. It’s making the case for a balance in power to maintain a firewall against unfettered Democratic power.

“Clearly, if the Democrats (win) both chambers, we’re going to see more attacks against fracking, oil and gas,” said House, the GOP chairman. “We’re going to see a bigger budget with more spending. Republicans are going to try to protect our top industries, like agriculture and oil and gas.”

In the House, competitive races stretch from Durango to Colorado Springs to the Denver metro area. Republicans hope to defeat Democrat Joe Salazar of Thornton, among others, while returning GOP incumbents including Kit Roupe of Colorado Springs and helping Katy Brown defeat Bridges in the close-in south Denver suburbs.

The top Senate races are in the Denver metro area, including Woods’ race in Jefferson County and two open seats in Arapahoe and Adams counties. In Aurora, Democrats are making a difficult play to upset Republican incumbent Sen. Jack Tate by running Tom Sullivan, whose son died in the 2012 movie theater shooting.

On the campaign trail, Woods said she doesn’t feel the pressure. She faces a rematch against Zenzinger, who lost by a fraction in 2014.

Both candidates are making an appeal to the middle-of-the-road voter in a district where most are unaffiliated with political parties — and the money is flowing.

Since starting the campaign, Woods has raised more than $192,600 – and had another $48,000 on hand – while Zenzinger has raised $224,364.

Even more is pouring in from political committees. Since the start of the year, more than $387,975 has been spent to oppose Woods – $125,000 of that from Washington, D.C.-based American Wind Action Colorado – finance records show, and another $137,000 to support her candidacy. A handful of groups led by Colorado Citizens for Accountable Government have spent more than $389,800 to oppose Zenzinger.

Still, the main challenge for both? Trying to get voters’ attention.

“I would say for about six months … they only really wanted to talk about the presidency,” Zenzinger said. “We tried to pivot to show them why this race, in their backyard, is a more important race. That the types of issues that come up at state government affect their everyday life.”

Denver Post staff writer David Migoya contributed to this report.

Updated Oct. 27, at 3:43 p.m. Because of inaccurate information from a source, a story on Page 1A Sunday should have said that certain expenditures by the Colorado Citizens for Accountable Government were to oppose Democrat Rachel Zenzinger in the race for state Senate District 19.