Now, one could argue that Mr. Santorum had every right to feel aggrieved during the debates, as he really was treated quite peripherally at times. But his campaign has since been characterised by an almost permanent sense of aggrievement - particularly towards the media.
Here is the latest example:
There are several points to make here. Firstly, someone like Mr. Santorum, who spends much of his political life talking about family values, should not be caught on camera swearing at reporters.
Secondly, Mr. Santorum has a habit of attacking the media for asking perfectly valid questions. He makes social issues a central theme of his campaign, and then complains when interviewers focus on social issues. In this instance, he attacks a NY Times reporter merely for asking him about a comment that he had made earlier.
In a wider sense, the above altercation calls Mr. Santorum's temperament into question. Can you imagine President Obama reacting to a question in this manner? How about Mitt Romney?
A presidential figure maintains his calm, no matter how unreasonable any given line of questioning may be.
Many Republicans appreciate attacks on the 'mainstream' media, and would interpret Mr. Santorum's performance as a display of passion and conviction. It is, in actual fact, a display of petulance and resentment. It is unbecoming, and it is certainly not presidential.