|Sec. of Agriculture Tom Vilsack (D-IA)|
Vilsack, for those unfamiliar, is probably the most successful Iowa Democrat (save Tom Harkin) in the past three decades. He served as mayor of Mt. Pleasant for a number of years before taking on two terms as Iowa's governor (sandwiched between the two governorships of Terry Branstad). He briefly made a play for president in 2008, but that dissipated shortly, and eventually became part of Obama's "Team of Rivals" cabinet as Secretary of Agriculture. In 2016, he was considered by most to be the runner-up to Tim Kaine in Hillary Clinton's veepstakes. At 68, he still seems to have some electoral ambitions (as does his wife, the quite popular Christie Vilsack who once made an unsuccessful run against Steve King), and would probably get right-of-first-refusal in the state were he to make a go of it against Ernst.
The problem for me is that this is a dance Democrats have attended before. While Republicans have been fine going back to the well in the past ten years for Senate candidates (look at former governor Mitt Romney being elected to the Senate from Utah just last year), Democrats have struggled, particularly with out-to-pasture former governors who want to make a play for the Senate, and then can't rebound because the state is too red. In the past four cycles alone, Democrats have tried this with Bob Kerrey, Evan Bayh, Ted Strickland, and Phil Bredesen. All four, like Vilsack, were popular in their day and won impressive victories for governor, but watched their states drift away from them to the point where they'd even struggle for the governor's race, much less the more partisan Senate contest. They all four looked like coups at the beginning of the race for the DSCC, polled well throughout the race and then they lost by double digits. While Iowa is bluer than most of these states, it has to be noted that even in the most favorable of environments they couldn't get Fred Hubbell across the finish line against Kim Reynolds, and that race also featured a moderate white guy against a dynamic young female conservative.
This should give anyone pause, and the stats for Vilsack are not strong even if you look further back. Since 2002 (the post Bush vs. Gore races), despite some truly great cycles (2006, 2008), only two out-of-office Democratic governors have picked up Senate seats from the other side (Mark Warner & Jeanne Shaheen in 2008), and only Shaheen did it by defeating an incumbent. While this is admittedly a small sample size, it has to be noted that Shaheen and Warner did this in states that were moving further to the left, which isn't the case for Iowa.
One could be right to play devil's advocate here and state "if Vilsack can't beat Ernst, no one can," and there might be some truth to that, but it's worth noting the few Democrats who did over-perform in red territory in recent years were largely younger, dynamic figures who could cut their own profile statewide rather than have decades of experience already doing it for them. Jason Kander, Beto O'Rourke, and Michelle Nunn all three come to mind as figures that may have lost, but did so by much smaller margins than any of these former governors and came much closer to success even with their state resistant to their party.
Iowa has no shortage of such candidates. Newly-elected Reps. Cindy Axne and Abby Finkenauer are clearly stars on the rise, though they may want to wait a cycle or two before jumping statewide, and new State Auditor Rob Sand feels cut from the same cloth as Kander or O'Rourke (and Josh Hawley proved this past year that voters don't really care if you office shop). State Senate Minority Leader Janet Peterson has been rumored for higher office for a while, and JD Scholten got a lot of press when he came close to besting Steve King in 2018. I personally think that while Vilsack is a good guy, the D's might be better off betting on a candidate whom every Iowa voter has an opinion on right off the gate, instead investing in a younger leader who might be able to better counter Ernst on the "who represents Iowa's future more?" question.