Please elaborate on these "tons of weaknesses" you speak of, and how they outweigh the strengths they bring to the table.
First of all, all the are very boring. It shouldn't matter but it does. As for specifics:
Rob Portman- Hes pro gay marriage. Not gonna happen in 2016. He was also Bush's OMB director. The Republican candidate will want to run from big budgets and high spending. You can't do this with the guy who oversaw the budget of the second biggest spender in US history. He's from Ohio, which makes him the only one of these three with any potential electoral benefit.
Cathy McMorris Rodgers- May I refer you to her state of the union response? Also, she's from a non swing state that she couldn't deliver, she's in the House of Representatives, and she brings nothing to the table. As someone pointed out on another thread, she doesn't pass the most important test which is will she be ready to be president on day one.
John Thune- Hes got a couple of Senate votes that conservatives won't forgive such as raising the debt ceiling and voting for TARP, but the biggest reason it won't be him is why would it be? Nobody will vote for the Republican because Thune is on the ticket, and there are a lot of other potentials who are equally qualified who people will show up for. If it's any establishment friendly senator, Rubio is much more likely.
The fact is that the VP nominee will most likely be a woman or minority, but it won't be a congresswoman from Washington who looks like she belongs on the cover of Better Homes and Gardens. The VP will also have to be someone who will get the base out, and none of these will do it.