DOVER — On Saturday, Republicans can end one of the longest continuous streaks of legislative dominance in the country and strike a blow against a Democratic majority that has controlled the state for the past eight years.

A special election for the 10th District Senate seat will determine whether Delaware’s Senate goes Republican or remains Democratic. Currently, there are 10 Democrats and 10 Republicans in the state Senate.

The 10th district seat has been vacant since Democrat Bethany Hall-Long resigned last month to become lieutenant governor.

Democrats have held the state Senate since 1973, one of the longest ongoing periods of control in the nation.

But that’s not all.

Over the past eight years they’ve been in charge of the state Senate, House and governor’s office. No one party has held all three for a longer period since the 1800s.

Republicans are leaning heavily against that streak of one-party rule, arguing that Democratic policies have harmed the state.

Republican John Marino is looking to give the Delaware GOP a huge victory by winning the district which stretches from Middletown to south Newark along the Maryland-Delaware border.

Mr. Marino faces Democrat Stephanie Hansen and Libertarian Joseph Lanzendorfer.

The Republican, who acknowledges he is an underdog, ran for the same office in the 2014 election cycle, garnering 49 percent of the vote.

The Democrat, Ms. Hansen, served as president of the New Castle County Council from 1997 to 2001.

The district includes about 16,100 registered Democrats, 10,100 Republicans and 9,400 independents.

A GOP win would represent a shift of power to an extent the state has not had since the Democrats took control of the House in 2008. It would also make any chance of raising the minimum wage over the next 16 months basically impossible and would increase the likelihood of success for a right-to-work law.

Republicans and Democrats would share control of the Joint Finance and Bond committees, as they did from 1985 to 2008.

The party in charge of the chamber sets the agenda for each legislative day, decides on committee assignments and chooses what bills go to what committees.

President Trump’s job approval rating, some observers contend, could also play a role in the election turnout. A Gallup poll conducted from Feb. 13 to Feb. 19 found 86 percent of Republicans approve of the job the president is doing, while 37 percent of independents and just 7 percent of Democrats do.

“If we want to be able to keep the federal Republican agenda from settling in our living room, we have to be able to have our own fortification here at home,” Ms. Hansen, the Democrat, said at a debate earlier this month.

She claims to be more fiscally conservative than the average Democrat. But Mr. Marino has crusaded against what he sees as unneeded and careless spending. Reducing the state government’s influence in the economy would help create jobs, he believes.

“We need to bring jobs back to the state of Delaware. We need to open our doors,” he said at the debate.

All three candidates said they support the Delaware Supreme Court’s ruling that certain provisions of the state’s death penalty are unconstitutional.

Each of the three also backs less school testing and increased support for drug addicts.

A win by Mr. Lanzendorfer, while unlikely, would represent a seismic shift and give him tremendous leverage.

“There wouldn’t be a roadblock as long as the Republicans and Democrats can reach across the aisle to work together to create the best legislation for Delaware,” Mr. Lanzendorfer said at the debate. “So, my presence in the Senate alone would create the best of both worlds and better legislation for all Delawareans.”

Big bucks and heavy hitters

Democrats are bringing out their big guns: Lt. Gov. Hall-Long, who represented the district for eight years, has campaigned for Ms. Hansen, as has Attorney General Matt Denn. Former Maryland Gov. Martin O’Malley, who campaigned for the Democratic presidential nomination last year, traveled east to speak at a rally on Ms. Hansen’s behalf earlier this month.

Even former Vice President Joe Biden has gotten involved by knocking on doors in the district.

For the Republicans, other senators, as well as some representatives, have been out door-knocking for Mr. Marino.

Ms. Hansen’s campaign is being managed by Eris Raser-Schramm, who has worked on several campaigns and once served as chief of staff for the House Democratic caucus.

Mr. Marino’s campaign manager, George Ball, left earlier this month, and the campaign is now being run by Rep. Kevin Hensley, whose district in southeast New Castle County encompasses part of the 10th. Mike Harkins, a former Delaware secretary of state who pleaded guilty in 2004 to mail fraud and false statements on a federal tax return, is also assisting the campaign.

With so much on the line, money is pouring into the race: As of Tuesday, $964,000 had been raised, leading to the possibility of a million-dollar race.

While it is not unheard of for $1 million to be spent on legislative races in some other parts of the country, namely around big cities, that’s a staggering sum for Delaware.

The money is a symbol of the attention being paid, both locally and nationally, to the 10th Senate District contest.

Ms. Hansen raised $387,000 as of Monday, while Mr. Marino had pulled in $142,000 and Mr. Lanzendorfer had picked up $3,000.

Third-party advertisers, or Political Action Committees (PACs), received a combined $432,000, with most of that coming from First State Strong. A pro-Hansen PAC formed last month, the group pulled in just over one-third of a million dollars.

Other groups — National Gun Owners Alliance, National Rifle Association Political Victory Fund, National League of Taxpayers, Delaware State Education Association Advocacy Fund, Right to Work Education Fund, Strengthening our Communities, Committee of One Million in Defense of Life and FirstStateFirst — raised comparatively smaller amounts, although most of the organizations helped the Marino campaign.

Plenty of money is being spent to ensure voters are aware of the candidates: Ms. Hansen, for instance, spent $175,000 on advertising with the Beytin Agency, a Virginia direct-mail company that promotes Democrats.

She has received plenty of out-of-state support, partly owing to the efforts of The Sister District Project. A group focused on helping Democratic candidates across the country, it has, along with the pro-Democratic group flippable, raised about $125,000 for Ms. Hansen, according to director of political strategy and policy Gaby Goldstein.

“Our model is really to look for strategic races for Democrats and provide a boost from grassroots volunteers and donors all over the country and sort of leverage these resources toward specific races,” Ms. Goldstein said.

The 10th Senate District is the first race The Sister District Project has aided. Ms. Goldstein said some of its volunteers have come to Delaware from nearby states to aid the Hansen campaign.

Republicans have gone on the offensive against the Hansen campaign, criticizing the First State Strong PAC. The PAC does not have to disclose its donors until the annual end-of-year reports. Because the organization was created this year, its contributors will remain secret until 2018.

Delaware Republican Party Chairman Charlie Copeland, who says the PAC broke the law by coordinating with the Hansen campaign, accused Ms. Hansen of “trying to buy this election” and “ride a wave of secret money into office.”

His complaint was investigated and dismissed by Election Commissioner Elaine Manlove, although the GOP claimed partisan politics were behind the decision and vowed to appeal it.

Looking back and ahead

Both the Republicans and Democrats have controlled the House and the governor’s office over the past 44 years, but the Senate has never been controlled by Republicans in that timespan.

As told by longtime political reporter Celia Cohen in the book “Only in Delaware,” the Democratic minority colluded with two dissatisfied Republican senators to surprise the rest of the chamber on the first day of session in January 1973.

The lieutenant governor “noticed that all of the Democrats were wearing red carnations, as were (the two Republican senators who would flip), but none of the Republicans were,” Ms. Cohen writes.

In a twist worthy of Game of Thrones, the trap was then sprung, with two Republicans voting with the Democrats and shifting the GOP out of power.

According to the book, Mike Castle, a Republican state senator who would go on to become governor and a U.S. representative, called it “an act of treachery.”

After the 1996 election, Democrats never had fewer than 13 members in the Senate until 2014, when Bryant Richardson defeated longtime Sen. Robert Venables, making the balance 12-9. The Senate peaked at 15 Democrats following the 2008 election, but the GOP has made a comeback, gaining one seat in each of the past four elections.

Just six states currently have both Democratic governors and Democratic legislatures.

The General Assembly has been at a near-standstill while both parties await the results of the race. While January is typically a slow month from a legislative perspective, this past month was especially quiet. Lawmakers openly admitted they were waiting for the special election to begin pushing legislation.

Over the next four months, proposals for marijuana legalization, reinstitution of the death penalty, creation of right-to-work laws and tax hikes are likely.

What happens with those legislative initiatives will depend, at least partly, on what happens Saturday.