Mitt Romney’s presidential campaign unveiled an app — you can download it here — this morning that will be the first place where they announce the former Massachusetts governor’s pick to be his vice president.

That means one thing: We are getting close.

With the day of reckoning rapidly approaching, we continue our “case for/case against” treatment of the top contenders for the VP pick. (If you missed our case for and case against Louisiana Gov. Bobby Jindal make sure to check them out.)

Today we make the case for Ohio Sen. Rob Portman, the presumed frontrunner for the veep slot. Later this week, we’ll make the case against him.

* The anti-Palin: It’s virtually impossible to overestimate how much John McCain’s pick of Sarah Palin as his vice president in 2008 looms over Romney’s selection process.

Everyone but McCain now concedes that Palin, who had spent two years as the governor of Alaska before she was plucked from obscurity, was ill-prepared for the job and, ultimately, undermined McCain’s “experience matters” argument against then Illinois Sen. Barack Obama.

The Romney team has let almost nothing about the candidate’s criteria for a ticketmate slip but one thing they have made clear is that competence and a readiness to do the job are by far the most important things he wants in a running mate.

Portman oozes competence. He’s spent time in both the executive and legislative branches and everywhere he’s served he’s won kudos for his abilities. It’s hard to imagine that even his staunchest Democratic opponents would be able to argue that Portman wouldn’t be up to the task of being vice president or even president.

Seen through the anti-Palin lens, the fact that Portman isn’t terribly sexy — politically speaking — also probably works in his favor. No one would argue that Romney picked Portman to spice things up. If Palin was a Hail Mary pass by McCain, Portman is a three-yard run up the middle.

A Portman pick could be sold as an example of Romney’s seriousness and focus not just on winning the presidency but also governing the country.

* Double threat: Most of the candidates still being talked about as Romney’s vice presidential pick have a similar resume to the former Massachusetts governor. That is, they are/were governors with very limited foreign policy experience. (And, no, we don’t count directing your state’s National Guard.)

That’s not the case with Portman who boasts real credentials domestically (head of the Office of Management and Budget, House Member, Senator) and internationally as the U.S. Trade Representative during the Bush Administration.

While the trade representative isn’t on the same level as, say the Secretary of State, Portman allies note that no one else on the short list can say they have sat at the table with other heads of state and negotiated real trade initiatives.

For a candidate like Romney, whose foreign trip exposed just how shaky he can be on international matters, having someone like Portman as a steadying influence could be quite beneficial.

(Worth noting: Obama picking Joe Biden was driven, at least in part, by this same line of thinking — that Biden knew global politics and policy and could be a major help to the president on those matters.)

* Ohio, Ohio, Ohio: Without a victory in Ohio on November 6, the electoral math gets very iffy for Romney. And, while the recent history of VP nominees helping to deliver a state or a region is decidedly dicey, there is an argument to be made that Portman actually can make a difference in the Buckeye State.

Portman spent 12 years representing the Cincinnati-area in the House before running statewide in 2010. His Senate campaign, which we covered closely on the Fix, was brilliantly run and while he would have almost certainly won even if it wasn’t — the year favored Republicans and Portman’s Democratic opponent was, um, not good — his 18(!)-point margin was eye-opening in such a closely divided state.

He proved his mettle (again) during the Ohio presidential primary earlier this year as Romney battled to beat back a surprisingly serious challenge from former Pennsylvania senator Rick Santorum. Portman was everywhere on the stump during the run-up to that vote, which Romney won by one percent.

And, Portman’s statewide organization drew praise for delivering the state to Romney — for good reason. Romney took his highest share of the vote in Hamilton County in Southwest Ohio — which Portman represented in the House — and netted more than 15,000 votes there, which was bigger than his overall margin statewide.

With 2012 shaping up more and more like 2004, a few thousand votes here and there in Ohio could make a big difference. (Massachusetts Sen. John Kerry lost Ohio by 118,00 votes in 2004 and, with it, the presidency.) There’s no one else being mentioned as VP who can make a better case than Portman that they can deliver real votes in a swing state.

* Low expectations: The rap on Portman is that he’s a boring guy who no one knows. That fact virtually ensures that if Portman is the pick the narrative that will emerge will be along the lines of “he’s more interesting that you might think!”. It’s just how these things tend to work.

Already Portman’s impersonation of a chicken and his near-death experience while kayaking are starting to build out the “this guy is interesting” storyline. (Heck, Buzzfeed already has produced this “15 interesting things about Portman” post.)

While Portman is never going to be the national rock star that a Marco Rubio or Chris Christie might be as VP, the expectations for him to be even vaguely interesting are so in­cred­ibly low that he will almost certainly exceed them.

Combine his deep resume with a sympathetic more-interesting-than-you-think narrative and Portman may well be the perfect Romney pick.