What is the difference between a Republican and a constitutionalist?

Answer 1

It depends...

In modern America, a republican usually just means someone who is a member of, or supports, or tends to support, the Republican party, whereas a constitutionalist believes there is some straightforward interpretation of the Constitution that should limit the policy choices of whoever is in power, Democrat or Republican, and will tend to support candidates who share this view. In this view, Republicans can vary widely in views, as long as they are closer to those of the Republican than Democratic party, whereas constitutionalists will vary by how they interpret various parts of the Constitution (are armed private citizens necessarily a "well-regulated militia") as well as weighing the various parts. In general, a Republican will desire a larger role for business in society, a stricter interpretation of the role of the military, more conservative social values, and a larger place for the legal system for enforcing limits on social behavior, whereas a constitutionalist need have no particular views on the place of large business, and may or may not advocate for a wider realm of personal freedom (the "pursuit of happiness").

A case can also be made that the above is a capital-R Republican, and a small-r republican believes in the principle of a republic, that is, electing skilled, competent leaders and trusting their policy decisions, as opposed to a small-d democrat, who believes in direct public participation in government. In these terms, the difference would have to do with how much power the government has to interpret the legal structure of law as defined by the Constitution in the interest of efficiency (i.e. a republican may support a immediate executive action were the country moving towards war, while a constitutionalist would insist that only Congress have the power to declare war, for example)

In other countries, and at different times in history, both terms meant different things, and were associated with different values.