Too far gone, ain't no way back
Did Gregg not know that his views were different from the President when he took the job offer? Why would you even entertain the offer if you were that committed to your principles? A conspiracy theorist may think that Gregg knew all along he was not going to go through with this, and that he just wanted to add another setback to the administration early on. I don't believe that myself, but Gregg's stated reasoning is illogical.
There are cynics that may say that Obama was trying to get one less vote against the stimulus package out of Congress. That would have been a bad idea, especially when you are putting that person in a position to carry out a major part of that package. Bottom line, this was just a bad idea. You knew it was bad idea when a Democratic governor of New Hampshire had to promise that he would appoint a Republican to replace Gregg. Mississippi Governor Haley Barbour would not have done that if the inverse situation occurred, I can guarantee you that.
The country is not in civil war, we are just in major conflicts overseas. We are not in a depression, just a major recession. Even after 9/11, Bush did not seek Democrats to fill any vacancies he may have had in key positions, he went with people he could trust. I have no idea what kind of relationship Obama and Gregg had when they served in the Senate together, but obviously it was not as sound as they thought it was.
Gregg is too far gone as a conservative to align himself with any Democratic administration. Most Republicans in this day and age are as well, so I would abandon, if I was the President, my search to bring Republicans into the Cabinet. There are many talented Democrats who were loyal to Obama during the campaign that can fill the remaining posts.
The stimulus package vote showed that the spirit of bi-partisanship is going to be a work in progress. For example, I was stunned by Senator Jim DeMint's (R-SC) comments on the Senate floor yesterday, when he kept implying that the American people were going to lose with this stimulus package. If that is the sentiment of the Republicans that voted against the package, then it is time to work the plan to make those dire predictions inaccurate. You can't do that with the foxes guarding the hen house.
As a former legislator, the President should know that an enemy on one piece of legislation may be an ally on another. Gregg would best serve the administration as an occasional ally on Capitol Hill, periodically stopping by the White House to offer his constructive criticism about policy proposals. That invitation should be offered to all Republicans in Congress consistently.
However, it is time to move on from bringing them into the Cabinet. Lincoln was great because he understood the time he was in. Obama needs to do the same.