One of the many important lessons I learned from sports was to maintain civility and respect for others even in heated competition. This lesson was reinforced when I competed in debate and by gaming hobby. When I became an academic, these lessons served me well by allowing me to easily behave in a professional manner: respectfully disagreeing with my colleagues.
While civil behavior is generally respected, I have taken some criticism in the past for being too civil and respectful—even when people are rude or awful to me, I rarely abandon my commitment to the social rituals of respectful and civil behavior. I will, however, admit that one reason why I do this is that I believe that honorable behavior in the face of rudeness demonstrates good character and shows the failings of the one who descends into rudeness. As such, I do hold to a moral foundation for civility as well as a bit of pride—not descending to the lower level is a point of honor for me.
Since I am a professional philosophy, I approach political differences as I would any theoretical dispute about values. That is, I maintain my professionalism even in in nonprofessional contexts. This serves me quite well in maintaining friendships with people who have vary different political values. For example, I have various running friends who are very conservative politically. However, we get along quite well even though I hold to many liberal and even anarchist positions in politics.
Because of my views of civility, it might be expected that I would roundly condemn the apparent incivility shown to members of the Trump administration, such as Sanders. After all, as you might infer from the above, I endeavor to avoid descending into incivility. Despite this, a case can be made that morally justifies such incivility.
I do believe that by default each person should be treated with basic civility—that is the starting point. People can, by their actions, change the level of respect they deserve. For example, people who treat others with respect are thus entitled to that respect in return. As another example, someone who is abusive and disrespectful reduces the respect they are due. Morality is also a key factor here—goodness is to be respected and evil is to be shunned.
In the case of political disputes, I do not assume that a person who disagrees with me must be evil and thus has no claim to respect or civility. If the person shares enough of the essential core values with me, I can accept that while we disagree they are a good person (or at least not evil) who is worthy of respect and civility. For example, while I disagree with my conservative friends on various issues, we still share essential core values about honesty, kindness, fairness, justice, democracy, and dogs. To use a specific illustration, my conservative friends and I both believe that people in need should not be abandoned to their fate. I tend to favor social programs that address this matter, while they tend to prefer a somewhat different approach. However, we agree with the basic ethics of the parable of the good Samaritan. So, my general point here is that civility is owed to those who have morally good core values even when there are heated disputes over political matters. Roughly put, the decent are entitled to decency.
In the case of people who are deficient in the core values and act in accord with their moral defects, they earn the disrespect of others. For example, someone who lies repeatedly and acts in other awful ways forfeits the claim to civility to the degree they are awful. As such, being uncivil to Sarah Sanders would be morally acceptable to the degree that she lies—which is regularly and extensively.
Another key part of civility is reciprocity. People merit civil treatment by being civil; they merit uncivil treatment by being uncivil. As such, people who are insulting, rude, and disrespectful have no right to expect others to treat them with civility and respect. Trump, for example, exemplifies uncivil behavior and hence has no right to expect civility from others. While he no doubt expects the respect due the office, my view is that the idea of respecting the office despite the behavior of the person in that office is absurd—on par with asking people to respect an ass in a nice car because the nice car is nice. A person is, rather, obligated to act in accord with the respect the office is supposed to command, otherwise it is they who are disrespecting the office and not those who disrespect the disrespectful occupant.
Thus, civility is only owed to those who are good (or at least not evil) or those who act with civility. Those who claim that the evil or uncivil should be treated with civility are in error, though people are free to be more civil than they are morally required to be.