Republicans were dealt another blow on Saturday night when Jim Marchant, who helped organize a national slate of Trump-aligned candidates aiming to take over state election systems, lost Nevada’s race for secretary of state to Cisco Aguilar, a Democrat. This result means that all election denier hopefuls of running for future elections in major battleground states had been defeated.

Democrats were also scoring victories elsewhere. Marie Gluesenkamp Perez a Democratic political neophyte beat Joe Kent in Washington. He was a hard-right veteran backed to Mr. Trump, who had defeated Jaime Herrera Beutler in a primary as a retribution for her vote against impeaching Mr. Trump. Mr. Kent’s loss was the second time Republicans had ousted a member of their party who backed impeachment, only to lose the seat to Democrats.

Even if Republicans hold the House, a Democratic Senate will prove to be a valuable asset for Mr. Biden. With the confirmation of nominees under Mr. Schumer’s guidance, the president will be able to confirm more judges for two more years.

Senate Democrats will be able protect Mr. Biden’s veto power by never bringing House legislation to a vote. Senate Democrats will have the ability to respond to political messaging bills passed in the House by using their own political messages. They can use bipartisan measures such as the infrastructure bill or the gun control bill, which were both passed out of the 50-50 Senate to try to force the House Republicans to act.

“Because the American people turned out to elect Democrats in the Senate, there is now a firewall against the threat a nationwide abortion ban, cuts to Medicare, Medicaid or Social Security, and the extreme MAGA Republican policies,” Mr. Schumer spoke Saturday night. “Republicans in the House should be on notice.”

In the past, the House has swallowed bipartisan solutions that were secured in the Senate. This is more likely when the Senate is in Democratic hands and the Congress is divided.

The Senate Democrats will be representing the administration in Congress when they pass bills to fund government and increase the statutory borrowing limit. Republicans, however, will most likely try to negotiate concessions under the threat from government shutdowns or a potentially catastrophic debt default if they take control of the House.