History does not suggest Democrats will lose control of the Senate, and so the question requires looking at the map. All 3 toss-up seats (WI, PA, NC) are now held by Republicans, and the Democrats can lose all of those and still maintain control of the Senate. The most likely outcome is Democrats winning the D-leaning states (NV, AZ, GA, NH) plus one toss-up state (maybe WI). But there will be some surprises, so the Republicans might have a 25% chance.

The president's party often loses seats in Senate mid-term elections [1], but that may not apply in 2022. A first term president might get a break. In the last 100 years, there were only 7 times the president's party did not lose mid-term seats: 1934, 1962, 1970, 1982, 1998, 2002, and 2018. But these follow a pattern. Many are the first mid-term after a party change in the president. Maybe voters give a president a pass when the previous president was of a different party. The first term of a president of a new party occured 11 times, with 5 times the president's party gaining Senate seats in the mid-term election, 5 times losing seats, and once with no change. The 5 losses were mostly reversion-to-means (60 to 53, 49 to 47, 61 to 59, 57 to 47, 57 to 51).

1922 Harding lost seats: 60 to 53
1934 Roosevelt gained seats: 60 to 69
1954 Eisenhower lost seats: 49 to 47
1962 Kennedy gained seats: 64 to 68
1970 Nixon gained seats: 43 to 45
1978 Carter lost seats: 61 to 59
1982 Reagan no change: 54 to 54
1994 Clinton lost seats: 57 to 47
2002 Bush gained seats: 49 to 51
2010 Obama lost seats: 57 to 51
2018 Trump gained seats: 51 to 53

So, the historical record does not suggest the Democrats will lose Senate seats in 2022, and the map needs to be looked at.

Using the excellent @m_collier map [2] with consensus leanings, there are 4 Democratic held seats (NV, AZ, GA, NH) and 6 Republican held seats (MO, OH, FL, WI, PA, NC) that are not safe seats. The 3 toss-ups (WI, PA, NC) are now Republican seats. Build a probability model, with 4 D seats each 65% likely to stay D, 3 R seats each 65% likely to stay R, and 3 toss-ups that are 50:50. Expected change in seats is:
D (4*.65 + 3*.35 + 3*.50) -4 = 5.15 - 4 = 1.15
R (4*.35 + 3*.65 + 3*.50) -6 = 4.85 - 6 = -1.15

Hmmm, that looks close. I built a monte carlo simulation in Excel to find the distribution of how many of the 10 seats Democrats might win:

Using the consensus leanings, Democrats need to win 4 out of the 10 seats in play, so they have a 16% chance of losing the Senate.

The Inside Elections leanings has 8 toss-up states (NV, AZ, WI, PA, NH, NC, GA, FL) now held by 4 Democrats and 4 Republicans. A simple binomial distribution has a 36% chance of the Democrats winning less than 4 seats.

The Cook Political Report [3] has 4 D seats leaning D (AZ, GA, NH, NV), 3 R seats that are toss-up (NC, PA, WI), and 2 R seats leaning R (FL, OH). If the Democrats hold all 4 D-leaning seats, they hold the Senate. Wikipedia [4] lists 8 battleground states, 4 held by D and D-leaning, 4 held by R with 1 R-leaning and 3 toss-ups.

History does not suggest Democrats will lose control of the Senate, and so the question requires looking at the map. All 3 toss-up seats (WI, PA, NC) are now held by Republicans, and the Democrats can lose all of those and still maintain control of the Senate. The most likely outcome is Democrats winning the D-leaning states (NV, AZ, GA, NH) plus one toss-up state (maybe WI). But there will be some surprises, so the Republicans might have a 25% chance.

The president's party often loses seats in Senate mid-term elections [1], but that may not apply in 2022. A first term president might get a break. In the last 100 years, there were only 7 times the president's party did not lose mid-term seats: 1934, 1962, 1970, 1982, 1998, 2002, and 2018. But these follow a pattern. Many are the first mid-term after a party change in the president. Maybe voters give a president a pass when the previous president was of a different party. The first term of a president of a new party occured 11 times, with 5 times the president's party gaining Senate seats in the mid-term election, 5 times losing seats, and once with no change. The 5 losses were mostly reversion-to-means (60 to 53, 49 to 47, 61 to 59, 57 to 47, 57 to 51).

1922 Harding lost seats: 60 to 53

1934 Roosevelt gained seats: 60 to 69

1954 Eisenhower lost seats: 49 to 47

1962 Kennedy gained seats: 64 to 68

1970 Nixon gained seats: 43 to 45

1978 Carter lost seats: 61 to 59

1982 Reagan no change: 54 to 54

1994 Clinton lost seats: 57 to 47

2002 Bush gained seats: 49 to 51

2010 Obama lost seats: 57 to 51

2018 Trump gained seats: 51 to 53

So, the historical record does not suggest the Democrats will lose Senate seats in 2022, and the map needs to be looked at.

Using the excellent @m_collier map [2] with consensus leanings, there are 4 Democratic held seats (NV, AZ, GA, NH) and 6 Republican held seats (MO, OH, FL, WI, PA, NC) that are not safe seats. The 3 toss-ups (WI, PA, NC) are now Republican seats. Build a probability model, with 4 D seats each 65% likely to stay D, 3 R seats each 65% likely to stay R, and 3 toss-ups that are 50:50. Expected change in seats is:

D (4*.65 + 3*.35 + 3*.50) -4 = 5.15 - 4 = 1.15

R (4*.35 + 3*.65 + 3*.50) -6 = 4.85 - 6 = -1.15

Hmmm, that looks close. I built a monte carlo simulation in Excel to find the distribution of how many of the 10 seats Democrats might win:

Democratic wins 0, 1, 2, 3, 4, 5, 6, 7, 8, 9, 10

probability 0%, 1%, 4%, 11%, 21%, 26%, 21%, 11%, 4%, 1%, 0%

Using the consensus leanings, Democrats need to win 4 out of the 10 seats in play, so they have a 16% chance of losing the Senate.

The Inside Elections leanings has 8 toss-up states (NV, AZ, WI, PA, NH, NC, GA, FL) now held by 4 Democrats and 4 Republicans. A simple binomial distribution has a 36% chance of the Democrats winning less than 4 seats.

Democratic wins 0, 1, 2, 3, 4, 5, 6, 7, 8

probability 0%, 3%, 11%, 22%, 27%, 22%, 11%, 3%, 0%

The Cook Political Report [3] has 4 D seats leaning D (AZ, GA, NH, NV), 3 R seats that are toss-up (NC, PA, WI), and 2 R seats leaning R (FL, OH). If the Democrats hold all 4 D-leaning seats, they hold the Senate. Wikipedia [4] lists 8 battleground states, 4 held by D and D-leaning, 4 held by R with 1 R-leaning and 3 toss-ups.

1. https://en.wikipedia.org/wiki/United_States_midterm_election

2. https://www.270towin.com/2022-senate-election/

3. https://cookpolitical.com/ratings/senate-race-ratings

4. https://en.wikipedia.org/wiki/2022_United_States_Senate_elections#Predictions

Very much into this.