If Democrats win both of Tuesday’s Senate runoff elections in Georgia, the Senate would be evenly split, 50-50, between the two major parties.

How would the Senate work if that happened?

U.S. history provides some answers — though not many. That’s because even splits in the Senate have been rare. And because the Senate has changed drastically since the last time it happened, in 2001.

1. How many times has this happened in U.S. history?

Only three.

In 1881, the Senate remained evenly divided for much of its two-year session. In 1954, it happened again — because of a senator’s death — but the even split lasted only a few months. And in 2001, the Senate was split 50-50 from January until June.

2. Who runs the Senate, if no party has a majority?

The party that holds the vice presidency. The Constitution makes the vice president the president of the Senate, with the power to cast the decisive vote in cases of a tie.

In 2001, for instance, Democrats had control at the outset, during the few days when Al Gore was vice president. Then, when Richard B. Cheney became vice president, Republicans took control.

This year, a 50-50 split would give control to the Democrats, with Kamala D. Harris able to cast the deciding vote as vice president.

3. What about the party that doesn't control the vice presidency? Is it just shut out?

Twice in the past — in 1881 and 2001 — the two parties have struck deals that allowed for some sharing of power. That left the out-of-power party with more leverage than a minority party typically has.

In 2001, for instance, the parties agreed to split committee memberships evenly — instead of overloading them with members of the majority party as usual. They also changed the rules so that, if a committee deadlocked on a bill, the bill could still be brought to a vote on the Senate floor.

Trent Lott (Miss.) — then the Senate’s top Republican — worked out that deal with then-Democratic leader Tom Daschle (S.D.). In an interview Tuesday, Lott said he wanted to avoid gridlock by giving Democrats greater influence.

“I could have been a horse’s rear, and said, ‘We have the majority, the hell with you,’ ” Lott said. “And we would have had daily warfare.”

That arrangement lasted about six months, until Democrats convinced Republican Sen. Jim Jeffords (Vt.) to switch to their caucus. Then, with a 51-49 majority, Democrats took control.

4. Could that sort of compromise happen again in 2021?

It’s possible. Neither Republicans nor Democrats have offered much detail about how they would handle a 50-50 split.

Several of the staffers who helped Daschle and Lott hammer out their power-sharing agreement are still working for the leaders of the current Senate, Mitch McConnell (R-Ky.) and Charles E. Schumer (D-N.Y.).

Before the 2016 election, when there was a chance of another 50-50 split, McConnell told reporters he would seek to use the 2001 agreement as a model.

“I think if we ended up 50-50 that we would simply replicate what we did” then, he said.

But the Senate has changed greatly since 2001, becoming sharply polarized and less prone to bipartisan cooperation.

“Tom Daschle and I used to talk more in a day than Mitch McConnell and Chuck Schumer do in a month of Sundays,” Lott said.

This week, for instance, some Republican senators say they will object to the counting of electoral votes for President-elect Joe Biden — turning one of Congress’s most basic, bipartisan functions into a venue for President Trump’s baseless claims of election fraud.

After that — and after two elections in Georgia that involved hundreds of millions of dollars in ad spending — would Democrats be willing to hand any of their newly won power back to Republicans?

5. If the Democrats have 51 votes, what could they pass?

With 51 votes, Democrats could confirm Biden’s nominees for Cabinet positions, for federal judgeships, and — if one came open — for a seat on the U.S. Supreme Court.

They could also use the legislative mechanism known as “reconciliation” to pass some legislation, if it is related to budgets or spending. That mechanism — which Democrats used to pass health-care reform in 2009 and Republicans tried to use to repeal it in 2017 — allows the Senate to pass legislation with just 51 votes.

But it is limited and could not be used to pass legislation unrelated to the budget. That sort of legislation is still subject to the filibuster rules, which require 60 votes for passage.

The Senate could, theoretically, change the rule setting that 60-vote threshold. But that sort of change seems unlikely: It would require support from every Democrat, and at least one — Joe Manchin III (W.Va.) — has said he won’t support it.