With the current Democratic majority in the House of Representatives at only nine seats, and the Senate's control by that party held solely by Vice President Kamala Harris's "tiebreaker" vote when needed, control of Capitol Hill is definitely in play this election day.
Pundits are focused on six Senate races where polls indicate "tossups" - situations where the undecided and "swing" voters will determine who gets to Washington.
One key race is in Georgia, where incumbent Democratic Senator Raphael Warnock is being challenged by novice candidate but football great Hershel Walker. Warnock took the seat in 2020 after a December runoff.
Another Senate slugfest is in Nevada. Republican polls put its candidate, Adam Laxalt in a narrow lead, but other polls give a slight edge to Democratic incumbent Senator Catherine Cortez Masto.
Wisconsin Republican incumbent Senator Ron Johnson was ahead in earlier polls, but recent ones are showing his race with Democrat Mandela Barnes is now much tighter.
In the small northeastern state of New Hampshire, incumbent Democratic Sen. Maggie Hassan holds a slight edge over Republican challenger Don Bolduc.
The "Keystone State" - Pennsylvania - has seen both parties fighting over an "open seat," one being vacated by a retiring senator, Republican Pat Toomey. The GOP has put up TV doctor and dual U.S,. - Turkish citizen Mehmet OZ, who has polled well despite the fight put up by his Democratic challenger, Pennsylvania Lieutenant Governor John Fetterman, who suffered a stroke in June but continued in the race.
Arizona's incumbent Democratic Senator Mark Kelly, a former astronaut, is being challenged by Republican Blake Masters. Forecasters give Kelly the edge in a state where the governorship may well be a win for Republican Kari Lake, who has strongly embraced Donald Trump and the former president's allegations that the 2020 presidential election results were not factual.
Because the Senate is presently 50 Republicans versus 48 Democrats and two independents who vote with the Democrats, a GOP gain of one seat cancels out VP Harris' tiebreaker vote and takes control of that chamber.
In the House of Representatives, the Democratic Party currently holds 222 seats while the Republicans control 213. So, it only takes five seats for the GOP to take control, and with it, the government's "power of the purse" since all federal spending bills originate in the House.
Because of that, Republican House wins would enable the opposition party to stop the Biden administration's spending on programs that have been enacted and supported by the Democrats.
There are fourteen "open" [incumbent not running again] House seats that political website fivethrityeight.com predicts could go to the Republicans.
When a president loses majority control of Congress, as happened to Barack Obama in the 2010 "Tea Party" election, Capitol Hill is able to block the White House's initiatives.
Ahead of today's election, some key Republicans said they would use their majority to launch a series of probes into a wide range of topics from Biden's departure from Afghanistan to investigations into his son Hunter Biden and allegations of his impropriety involving Ukraine and the corporation Burisma.