In 2016, every single Senate race went to the candidate of the same party that those states voted for in the presidential election, according to a new analysis by the Democratic group One Country Project, provided exclusively to Axios.

Why it matters: That's never happened before, since at least 1984. And the data shows that's not great news for Democrats heading into the 2020 elections.

The purpose of One Country Project is to help the Democratic Party win back rural voters ahead of the 2020 cycle, so they're squarely focused on Trump country.

The big picture: Republicans have a significant head start in the race to keep control of the Senate, per this group's analysis.

Because of their stronghold in rural areas, and based on previous presidential election results, the GOP has a 40-seat, "built-in base in the Senate."

Compare that to just 26 Senate seats that Democrats are best positioned to win.

That's prompting some Democrats — like former North Dakota Sen. Heidi Heitkamp, who's a founding member of One Country Project — to sound the alarm ahead of 2020.

"[U]nless we do a better job engaging rural Americans, Republicans will have a massive head start in every race for a Senate majority and a lock on enough seats to stand in the way of a Democratic president’s agenda," Heitkamp said. "If nothing changes, Democrats will never have more than a hope and a prayer of eking out a slim Senate majority — at best."

By the numbers: Those "built-in" advantages are based on each party's "base" states, where they won the presidential vote by 10 percentage points or more in the last election.

Democrats won 13 states by that measure in 2016, which translates to 26 Senate seats.

Republicans won 20 states by that measure, which gives them an advantage in 40 Senate races.

In 2020, there are 22 Republican incumbents up for re-election compared to just 12 Democratic senators.

Conventional wisdom says that the GOP should be more vulnerable given those numbers. But since these Republican incumbents mostly come from states that heavily support President Trump — and considering Senate results increasingly match presidential results — this could pose another challenge for Democrats.

View the full One Country Project analysis