Craig Kimbrel still has to pass his physical, but it looks as though he's headed to Wrigley Field after agreeing to a three-year, $43 million contract with the Chicago Cubs, earning $10 million the remainder of this season and $16 million in 2020 and 2021 (with a $1 million buyout/vesting option for 2022).

As successful as Theo Epstein and Joe Maddon have been, the search for stability in the ninth inning has been a revolving door even as the Cubs made the postseason the past four years. To review:

2015: Hector Rondon had a 1.67 ERA and 30 saves and was the closer in the playoffs.

2016: Rondon led with 18 saves, but the club traded for Aroldis Chapman and he finished with 16 saves and was the closer in the playoffs.

2017: With Chapman departing as a free agent, Epstein acquired Wade Davis from the Royals and he had 32 saves with a 2.30 ERA.

2018: With Davis departing as a free agent, the Cubs signed Brandon Morrow as a free agent. He pitched well with 22 saves and a 1.47 ERA, but didn't pitch in the second half and Pedro Strop took over as closer and finished with 13 saves.

2019: With Morrow still unable to pitch, Strop and Steve Cishek have shared the closer duties.

Entering Wednesday's action, the Cubs' bullpen actually hadn't been terrible, ranking eighth in the majors (and third in the National League) with a 4.02 ERA. I like to look at Win Probability Added for bullpens, as that statistic factors in game score and clutch results better than raw ERA, and the Cubs ranked 16th in the majors. OK, so the Cubs' bullpen was middle of the pack. It probably feels worse than that, but there have been a lot of bad bullpens this year. Editor's Picks Better late than never, Kimbrel is the closer the Cubs needed

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So Kimbrel should help. We all know Kimbrel struggled with his control last October, and while batters hit just .146 off him in the regular season, he did allow a career-worst 18 extra-base hits. The 31-year-old is not a sure thing to remain one of the best closers in the league, but he should be a clear upgrade over Strop and Cishek, and that pushes them into other roles. I would say that will help Maddon with his matchups except the Cubs don't really have a reliable lefty in the pen.

The ripple effect is how the other teams in the NL Central might eventually upgrade their own rosters. With the Cubs holding on for a 9-8 victory Wednesday over the Rockies and the Brewers losing to the Marlins, the Cubs hold a one-game margin over Milwaukee and 3½ over St. Louis, with the Pirates and Reds a bit further back. The Reds, at 28-32, hold the second-best run differential in the division, so don't write them off.

Let's see where each team needs to improve:

Milwaukee Brewers: Milwaukee made one of the more debatable decisions of the season earlier this week when it activated Travis Shaw from the injured list and sent Keston Hiura back to the minors even though Hiura was hitting .281/.333/.531 while Shaw had hit .174 with 50 strikeouts in 41 games. I get that it's hard to turn Shaw into a bench player after he hit 30-plus home runs the past two seasons, but the Brewers clearly have faith that Shaw's issues were injury-related. I imagine Shaw will have a short leash to get going or Hiura will quickly be back up. 'You owe it to the game' Brewers slugger Christian Yelich is driven to show his MVP season was anything but luck. Story »

Anyway, the Brewers will be looking to upgrade the rotation that ranks 20th in the majors with a 4.66 ERA. Zach Davies has been huge with a 2.20 ERA, but that's not sustainable, and Jhoulys Chacin and Gio Gonzalez just landed on the IL. Milwaukee did get a possible boost Wednesday with the return of Jimmy Nelson, who made his first major league start since September 2017, when he hurt his shoulder running the bases. Remember, he had developed that year into one of the top starters in the NL.

Against the Marlins, he gave up a run in the first inning and then a grand slam to Brian Anderson in the third. His four-seam fastball velocity topped out at 94.0 mph and averaged 92.4 compared to 97.8 and 94.1 in 2017, but it's one game and he had a busy day, as his twin daughters, born prematurely, went home from the hospital earlier (plus it was his birthday).

Possible targets: Dallas Keuchel, Madison Bumgarner, Marcus Stroman. There isn't going to be much starting pitching out there, although the market could get interesting if the Indians fall out of the race and make Trevor Bauer available. Keuchel would be the easiest addition since it costs only money to sign him. Bumgarner is a free agent and 2014 is five years ago, so there's no guarantee you're getting that postseason ace you might think you're trading for -- he has a 4.05 ERA for the Giants -- but, man, I think Craig Counsell would love to send him out there in a Game 1 against the Dodgers.

St. Louis Cardinals: The Cardinals are eighth in the NL in runs per game and seventh in runs allowed per game. As suggested by their 30-29 record and plus-16 run differential, the Cardinals are middle of the pack in offense, middle of the pack in starting pitching and middle of the pack in the bullpen. This has kind of been the issue with the Cardinals the past three years as they've missed the postseason: They never have any huge weaknesses, but they haven't had enough big positives to reach October.

Really, the Cardinals' best hope is to have their best players perform better: Matt Carpenter is hitting a lukewarm .225/.337/.402 and Paul Goldschmidt is at .271/.359/.449, below his usual level. Miles Mikolas hasn't been the same guy as last season, with a 4.41 ERA this season. Jordan Hicks and Andrew Miller haven't been lights-out, as anticipated. The rotation coughed up way too many home runs in April but was better in May. The return of Carlos Martinez will help the bullpen, and I'm still expecting Jack Flaherty to go on a dominant run.

Possible targets: Pitching ... of some sort. I would tend to think a starter is more likely -- I mean, a bullpen with Hicks, Martinez, Miller, John Gant (who has been lights-out) and John Brebbia should be good enough. Here's a wild thought: If Carpenter continues to struggle and the Cardinals are still close in July AND the Nationals continue to falter, how about going after Anthony Rendon and making Carpenter a utility guy down the stretch? The Cardinals do have some pitching depth and have a couple minor league third-base prospects who should interest the Nationals.

Pittsburgh Pirates: FanGraphs gives the Pirates a 5 percent chance of making the postseason. Only the Giants have a worse run differential in the National League. This is the Pirates. They're not going to make a major move.

Cincinnati Reds: The Reds are in an interesting position because they essentially went all-in for 2019 with the Dodgers trade and the Tanner Roark and Sonny Gray deals. Pitching coach Derek Johnson has done wonders for this staff, as the Reds are neck and neck with the Dodgers for fewest runs per game -- a minor miracle considering their home park and how bad the rotation has been the past several years. Kris Bryant is crushing it with his new bat Notice anything different about Kris Bryant? Here's how a mid-at-bat change to an ax-handle bat helped ignite the Cubs slugger. Jesse Rogers

The surprising aspect is the Reds have struggled to score runs -- and it's not all Joey Votto's fault. Jose Peraza has been terrible, Jesse Winker hasn't been that .400 OBP guy like he was last year and Yasiel Puig has been a big fat zero with 0.0 WAR. (In fact, how bad has that Dodgers trade been: Matt Kemp was released, Alex Wood hasn't pitched and Puig has been a flop.)

Trouble is, how do you upgrade? You're not going to bench Votto and you're not going to bench Puig. Derek Dietrich is slugging .700 and has taken over as the left-handed part of the platoon at second base. Much like the Cardinals, the Reds just need their good players to play better. Plus, if you look at the team likely to be making a deal -- the bad teams in the American League -- none of them will have much in the way of position players on the market.

Possible targets: The Reds could look into the starting pitching market to upgrade from Anthony DeSclafani, and a reliever like the Giants' Will Smith would help. Stroman would be a potential fit as he's signed through 2020 and his ground ball game fits in the Great American Ball Park. They could go for some outfield depth with somebody like Hunter Pence, having a resurgent year with the Rangers, or Adam Jones of the Diamondbacks (although the D-backs have a better record right now than the Reds).

Will the Kimbrel signing force teams to move faster than usual on the trade deadline? Possibly. The Cubs already rated as the division favorite -- FanGraphs gave them 67 percent odds to win the Central before adding Kimbrel -- so there is certainly added incentive now for the Brewers and Cardinals to do something.