Ezra hits upon a couple of good points in this piece, though I disagree with some of his points as well. He writes:

In 2009, the incoming Obama administration tapped Colorado Sen. Ken Salazar to head the Interior Department, Arizona Gov. Janet Napolitano to lead the Department of Homeland Security, and Kansas Gov. Kathleen Sebelius to lead the Department of Health and Human Services.

Colorado was — and is — a swing state. Napolitano was hugely popular in Arizona, where Sen. John McCain, whose numbers looked weak, was up for reelection in 2010. Sebelius was massively popular in Kansas, Where Sam Brownback, one of the incumbent Republicans, was retiring.

So the White House removed a popular incumbent in a closely divided state and then knocked out their party’s top draft picks in Arizona and Kansas. Democrats ended up almost losing the Colorado seat and barely contesting the Arizona and Kansas seats.

This argument was popular in the runup to the 2010 midterms, in which the Senate math greatly favored Republicans. In retrospect, though, it seems highly unlikely that either Napolitano or Sebelius would have joined the Senate that year, and neither one had especially good prospects for elevation beyond a federal post. In a counterfactual scenario where Tom Daschle became Health and Human Services Secretary and Sebelius stayed in Kansas, history would have played out roughly the same: the rise of the Tea Party as the product of racialized disapproval of Obama’s agenda and a lousy economy would still have occurred, the Town Hall Disruptions would have happened, and while Daschle might have helped move the ACA along a little bit more quickly, Obama was still intent upon staking the whole thing on bipartisanship that simply wasn’t in the cards. It’s impossible to imagine Sebelius winning against the 2010 wave in Kansas, any more than (also-popular) Governor Pataki would have been able to win the New York Senate seat in 2006. Now, Arizona is a little bit less Republican than Kansas, and it’s possible that Napolitano would have been able to highlight McCain’s utter surrender to extremists in order to hold onto his nomination. But the red wave simply makes me think that she would have been successful either, as Napolitano’s approval would probably have wilted if she’d had to govern during the state’s horrible economic period following the housing collapse in 2007-8. Indeed, Gov. Brewer’s poll numbers were lousy until she signed her signature immigration bill and aroused the anti-immigration vote. Looking back, the two most unfortunate Cabinet appointments made by Obama were Salazar, whose elevation caused an unnecessary risk, and Tom Vilsack, who could have run a strong challenge to demented Twitter Granddad Chuck Grassley in 2010. But the fundamentals of 2010 simply weren’t very favorable to red-state Democrats.

Ezra ties this to the possibility of Obama giving John Kerry a Cabinet slot, followed by a possible Scott Brown resurgence in Massachusetts. I must admit, #SecDefKerry has surprised me. I see no real logic for the appointment since there are plenty of other candidates with better qualifications who wouldn’t have any chance of giving up a Senate seat, so why give it to someone who had a chance of giving up the seat? But it’s so strange I’m inclined to think it isn’t just something to make Kerry feel he’s being considered. In any event, assuming Brown had an interest in Kerry’s seat, it’s unclear that he still has the political juice to win it, as his favorability took a significant hit during the campaign. After excluding all partisan polls and crummy university polls that showed Brown winning days before the election, here’s the chart:

It should be noted that Warren’s greatest argument against Brown–that is, preserving a Democratic Senate–no longer applies, which would help him. But his standing with the electorate has significantly diminished, and an opponent who is hungry and takes nothing for granted would have a strong shot. Brown’s career in Massachusetts politics ended when he said he admired Antonin Scalia, I strongly suspect.

Ezra also writes this:

And given that Democrats are defending 20 Senate seats in 2014 and Republicans are defending only 13, [Scott Brown] may be the difference between Harry Reid as majority leader and Mitch McConnell as majority leader.

Yeah, except a five-seat win under normal circumstances (they’d need to go from 46 to 51, since Biden could break ties with 50) would be unlikely. Democrats do have a large number of red-state seats in 2014, but most are incumbents who are running again and none are pushovers. If the economy continues to show signs of improvement, the 95% incumbency retention would make it a very difficult proposition for Republicans to retake the Senate. A lot of retirements could help, but at this point the only question marks are Johnson of South Dakota and Rockefeller of West Virginia. If both agree to run again, the odds of Republicans retaking the Senate would be long indeed, even if Brown were to make a comeback. And I don’t figure 2014 to be a wave election, with a gently improving economy and an end to the Afghan War the most likely political backdrop.

Personally, I think that giving Kerry a Cabinet post is a risk, but not necessarily a huge one. If it were up to me I’d just as soon take no risk, but I don’t really think there’s a case to be made that Obama has cost Democrats a lot of obvious Senate wins with his appointments either. Which isn’t to say he couldn’t start now…