Opinion polls suggest Democrats have a good chance of winning control of the House and Senate in midterm elections already underway with early and mail voting. But opinion polls aren’t infallible.

President Trump’s surprise victory over Hillary Clinton in 2016 should remind us that polls and pundits can be wrong.

My fellow Democrats shouldn’t assume that a blue wave will sweep away Republican majorities in both congressional chambers or wash the red tide of supermajorities in state houses which we have abandoned in multiple presidential seasons.

Democrats need to mount an all-out get-out-the-vote effort from now through Election Day to flip the House and Senate — a strong get out the vote campaign, followed by a post-election defense of Democratic victories that may be challenged by Republicans.

And while frequent and occasional Democratic voters are as vital as a roux in a creole gumbo recipe, the Democrats need extra seasoning this fall.

We must reach out to independents and Republicans who are disgusted by Trump’s repudiation of traditional Republican positions on a broad range of issues, and by his extremism, incompetence, dishonesty, corruption and failure to deliver on many of his 2024 campaign promises.

As a first step, Democrats still have time to educate voters so they understand the rules governing registration, voter identification and ballot access in their states. Requirements vary across the country. Voters should consult reliable, state-specific information before heading to the polls. That is available here.

Democrats should also encourage voters to cast their ballots early by mail or in person. Bad weather, illness, a heavy workload, traffic jams, long lines at polling places and other unexpected factors can prevent some voters from casting ballots in person on Election Day. Where permitted by law, campaigns and civic organizations should assist voters who need help in returning ballots by mail or in drop boxes.

For years, Republicans and conservative allies have built formidable Election Day turnout operations, relying on volunteers at the precinct level and extensive organizing in the weeks leading up to an election. Democrats must match that intensity.

Pro-democracy organizations, including the No Kings movement, are working to boost voter turnout nationwide. As No Kings says on its website: “Power belongs to the people, but only if we use it.”Democrats would be wise to strengthen their own field operations while working alongside civic organizations that encourage voting. These efforts will be especially important in reaching young voters and people who often don’t vote.

Infrequent voters should be encouraged to check their registration status now. Voters should confirm their polling locations, learn their state’s deadlines and requirements and make a concrete plan to cast their ballots. The group Vote411 provides voters with useful information on its website about how to make a plan to vote.

Unfortunately, Democrats must prepare for the possibility that Trump and his allies will challenge election results, spread disinformation and sow division when Republican candidates lose.

The Jan. 6, 2021 attack on the U.S. Capitol by Trump supporters trying to stop Congress from certifying Joe Biden’s legitimate victory remains a sobering reminder of the importance of respect for the will of the voters and a peaceful transfer of power.

Democrats must be ready to respond to Republican attempts to undermine confidence in legitimate election results, while ensuring that every challenge to Democratic victories is addressed through lawful procedures and established safeguards. Democrats must also remain attentive to changes in election administration and redistricting that could affect the competitiveness of congressional races. The integrity of our elections depends on fair rules, transparent procedures and public confidence in the results.

Trump wants us to believe that any election he loses, and many elections lost by Republicans he supports, must be rigged. This is not true.

I have campaigned for Democrats for decades, served twice as interim chair of the Democratic National Committee and remain a member of the DNC. I have never tried to rig an election, and I don’t know any Democrat who has.

Even outstanding candidates can lose elections. I’ve seen this happen many times to Democrats I supported, such as when Vice President Kamala Harris ran for president against Trump in 2024.

I know Harris would have made a great president, but like her, I accepted the judgment of American voters who returned Trump to office. Unless candidates run unopposed, all elections have to end with losers as well as winners.

America has a long tradition of elections administered by Democratic and Republican state and local officials. Protecting that tradition is a responsibility that transcends party. It is what makes our country exceptional and the leader of the free world.

So, my final bit of advice is for Americans of every political persuasion: Believe in our democracy and in free and fair elections.

As former British Prime Minister Winston Churchill said in 1947, two years after his Conservative Party lost an election that removed him from office: “No one pretends that democracy is perfect or all-wise. Indeed, it has been said that democracy is the worst form of government except for all those other forms that have been tried from time to time.”

Donna Brazile is a political strategist, a contributor to ABC News and former chair of the Democratic National Committee. She is the author of “Hacks: Inside the Break-ins and Breakdowns That Put Donald Trump in the White House.”