Whether presidential candidate Rick Santorum was hoping to rally a segment of the Republican primary electorate or sincerely expressing a deeply held view is unknowable. But the former Republican senator’s repudiation of John Kennedy’s assertion, made two months before he was elected as the nation’s first Catholic president, that church and state must remain separate is troubling.

What is most troubling about Mr. Santorum’s pronouncement is that it seems to deliberately pick a fight where peace has reigned for several years. The senator also seems to confuse — deliberately? — the roles of faith principles and political principles in governing.

“’I don’t believe in an America where the separation of church and state is absolute,” Mr. Santorum said. “The idea that the church should have no influence or no involvement in the operation of the state is absolutely antithetical of the objectives and vision of our country.” Referring to an earlier public comment he made about President Kennedy’s 1960 speech to Protestant leaders, Mr. Santorum — also a Catholic — was even more blunt: “To say that people of faith have no role in the public square? You bet that makes you throw up,” he said.

The late president was a deeply flawed man, as seen more clearly in the recent revelation by a woman who claims to have had a sexual relationship with Mr. Kennedy while she was a White House intern. But what he actually said about the role of faith is very different than the context Mr. Santorum suggests. Mr. Kennedy raised eyebrows being a Catholic because in many parts of the country, adherents were a small minority. And there was a real fear that he would take orders from the pope, a foreign potentate of sorts.

“I believe in an America where the separation of church and state is absolute,” candidate Kennedy said, “where no Catholic prelate would tell the president — should he be Catholic — how to act, and no Protestant minister would tell his parishioners for whom to vote; where no church or church school is granted any public funds or political preference; and where no man is denied public office merely because his religion differs from the president who might appoint him or the people who might elect him,” Mr. Kennedy said.

“I believe in an America that is officially neither Catholic, Protestant nor Jewish; where no public official either requests or accepts instructions on public policy from the pope, the National Council of Churches or any other ecclesiastical source; where no religious body seeks to impose its will directly or indirectly upon the general populace or the public acts of its officials; and where religious liberty is so indivisible that an act against one church is treated as an act against all,” he continued.

Nowhere in the speech did Mr. Kennedy suggest that his faith would not guide him or sustain him, as faith has no doubt guided and sustained many presidents through dark and challenging times.

Understanding what turns Mr. Santorum’s stomach is important. His public remarks suggest he believes the church as an institution should have an influence in the public square. A church expressing its views on issues is not objectionable, though there is a line that churches may cross which should threaten their tax-exempt status. Individuals, relying on their faith-inspired values and principles, also are welcome to speak on candidates and issues.

But the line must be drawn to stop elected officials from creating a conduit between church dogma and public policy. It is not clear where Mr. Santorum, were he to be elected president, stands on this matter.

Mr. Kennedy’s words more than 50 years ago articulate a litmus test to which Mr. Santorum ought to submit: “I believe in a president whose religious views are his own private affair, neither imposed by him upon the nation, or imposed by the nation upon him as a condition to holding that office.”