• Most US House races were called on Election night or in the days after.
• But the contest between GOP Rep. John Duarte and Democrat Adam Gray remains too close to call.
• The outcome will matter in a House narrowly divided along party lines.

Republicans are headed into 2025 in control of the presidency, the Senate, and the House of Representatives.

But there's still one outstanding House race yet to be called. And its outcome could impact President-elect Donald Trump's ability to push through his agenda.

In California's 13th Congressional District — anchored in the state's agriculture-rich Central Valley — former Democratic state Assemblyman Adam Gray leads incumbent GOP Rep. John Duarte by just 227 votes with an estimated 99% of the votes counted.

Gray has 105,083 votes, compared to 104,856 votes for Duarte, according to the California Secretary of State's office. The race is a rematch of their 2022 contest, which saw Duarte ultimately defeat Gray by 564 votes out of nearly 134,000 ballots cast.

Republicans needed 218 seats to control the chamber and have already won 220 seats, while Democrats currently have 214 seats. So, the seat won't affect the balance of power. But in the narrowly divided House, the margins will matter.

Here's a look at why this race has taken so long to call and why its outcome remains significant.

Ballots can arrive after Election Day

While many states won't count ballots that arrive after Election Day, California law allows ballots postmarked by Election Day to be counted if they arrive up to seven days after the polls close.

Due to the number of competitive US House races in California, a state with over 22 million registered voters, control of the chamber can theoretically rest on the Golden State alone.

Headed into the general election, this was a high probability, especially with Vice President Kamala Harris — a former California state attorney general and US senator — at the top of the ticket.

The 13th District encompasses Merced County, much of Madera County, and parts of Fresno, San Joaquin, and Stanislaus counties. So several jurisdictions play a role in counting the ballots, and election officials must also examine voter signatures and open envelopes.

Gray led in the vote count on Election night, but Duarte then pulled ahead and had been ahead for weeks before Gray regained a razor-thin lead on November 26.

For California voters that need to fix technical errors on their ballots — also known as ballot "curing" — the deadline is December 1.

The GOP will have to run a tight ship

Should Gray emerge as the winner of the race, Republican House Speaker Mike Johnson of Louisiana will be faced with a slim 220-215 majority.

That's before the expected departures of Rep. Elise Stefanik of New York, who Trump selected to be the next US ambassador to the United Nations, and Rep. Michael Waltz of Florida, who Trump selected to be the next national security advisor. Also, the seat of former Rep. Matt Gaetz of Florida is set to be filled in an April 1 special election.

Johnson doesn't have a lot of room to maneuver as Trump will expect Republicans to greenlight his agenda.

Attempting to push through heavily conservative legislation when more centrist Republicans can potentially pump the brakes on certain bills will make every vote matter.

So, a Gray or Duarte victory could have a considerable impact on Washington over the next two years.