Justice John Marshall, in "McCulloch vs. Maryland, in 1819:
"Let the end be legitimate, let it be within the scope of the constitution, and all means which are appropriate, which are plainly adapted to that end, which are not prohibited, but consist with the letter and spirit of the constitution, are constitutional."
While the end of protecting America from terrorists and enemies, both domestic and foreign, is legitimate and constitutional, the means to those ends that TSA has adopted recently, namely the coercing all passengers passing through airport security to submit to the body scanners or invasive pat-downs are unconstitutional, blatantly violating the 4th Amendment.
The 4th Amendment secures and protects all individuals and their persons, meaning their individual bodies from invasive and warrant-less searches and seizures by the government, whether local, state, or federal. TSA cannot coerce al passengers to submit to their invasive searches because they do not have warrants to do so. And even if TSA had warrants for everyone, their would be invalid warrants because they would have to be based off of probable cause, or rather, clear evidence that an individual is committing a crime or will commit a crime, which they do not and cannot have. Going through security at the airport in order to get to one's flight is not a crime. Nor is the very slim potential of everyone having some dangerous object on them or means of harming others on another airplane evidence or probable cause enough to issue warrants for all to be searched. Warrants must be explicit in their probable cause and evidence, must be specific in who, what is going searched and when and where, and for what reason. They must also be specific in who and what will be seized, as well as where, when, and for what reasons.
Therefore, because these means that the TSA has adopted in order to achieve the end of protecting Americans from terrorists and enemies, both domestic and foreign, are unconstitutional, violating the 4th Amendment, they may not be used by TSA, no matter how effective people may think they are or no matter how much people may want them. We must always be bound by the Constitutional, and we must always uphold it's every word and clause.