The US Senate has had 1,994 members since 1789, and there have been great Senators, mediocre Senators, and wretched, horrible Senators.
One third of the US Senate comes up for election in every even numbered year, so the entire Senate is elected over a six year period.
Right now, 20 Republican seats are up for 2022, compared to 14 Democratic seats.
With a 50-50 Senate, only the fourth time in history that the Senate has been evenly divided, after 1881-1883, 1953-1955, and 2001-2003, it is a crucial time for both parties, wishing to gain a majority of the Senate.
Five Republicans are retiring—Richard Shelby of Alabama; Roy Blunt of Missouri; Richard Burr of North Carolina; Rob Portman of Ohio; and Pat Toomey of Pennsylvania.
Three Republicans have not announced if they will run for reelection in 2022–Lisa Murkowski of Alaska; Ron Johnson of Wisconsin; and John Thune of South Dakota.
Only one Democrat, Patrick Leahy of Vermont, has not yet announced if he will run for reelection in 2022.
Twelve Republican Senators are running for reelection, as compared to 13 Democratic Senators.
The big goals for Democrats is to defeat the following five Republicans:
Marco Rubio of Florida
Rand Paul of Kentucky
Ron Johnson of Wisconsin, if he runs
Chuck Grassley of Iowa
Mike Lee of Utah
Also, the hope is that Democrats can win the seats of retiring Senators as follows:
Roy Blunt of Missouri
Richard Burr of North Carolina
Rob Portman of Ohio
Pat Toomey of Pennsylvania
So now a year before the elections, there is the theoretical possibility of the Democrats gaining up to nine seats, but truly, that is being highly idealistic, and unlikely to occur.
It all comes down to what Democratic seats are in danger, which would seem to include the following:
Mark Kelly of Arizona
Raphael Warnock of Georgia
Catherine Cortez Masto of Nevada
Maggie Hassan of New Hampshire
So the odds are in favor of the Democrats in theory, having a chance in nine states, while the Republicans have a chance in four states.