With Democrats and Republicans on Capitol Hill confronting one another over Senate filibusters, Social Security and the ethics process, the pressure to toe the party line is intense. More than once, I’ve heard a Member of Congress lament that despite his better judgment, he’ll vote the way his leadership demands because he wants to be a “team player.”

This is, of course, nothing new. “You’ve got to go along to get along” might as well be engraved in the desktop of every Member; even freshmen arrive well aware they’ll go nowhere fast if they start out by bucking their party leadership.

There is an old story about Lyndon Johnson meeting with a group of new Members while he was president. One of them asked Johnson for advice on how to vote during his time in office. The president responded that he should do whatever his party leadership told him. Outside the meeting a few minutes later, a reporter asked Johnson if he’d given any advice to the new legislators. Surely, Johnson replied, “Always vote in the best interests of the American people.”

That pretty well captures the realities of Washington. Out in the glare of the television lights, “the people’s” interests are trotted out and given the starring role. But behind closed doors, there’s a gaggle of competing interests every legislator must weigh. If the president is of one’s party, there’s a natural desire to support him. So, too, with a party’s leaders, who can advance a Member’s career and make it easier to help constituents. Then there are the constituents themselves, campaign contributors, lobbyists: All of them have some claim on a lawmaker’s loyalties.

It’s easy enough to sort all this out when, say, the interests of the party and the district coincide. But what about when the decisions are tough, when the various claims on one’s loyalty conflict? Is there no single standard by which a Member of Congress can steer?

I think there is a standard, one that every Member is familiar with, because it’s contained in the oath he or she swore upon taking office. “I do solemnly swear that I will support and defend the Constitution of the United States against all enemies, foreign and domestic,” it goes; “that I will bear true faith and allegiance to the same; that I take this obligation freely, without any mental reservation or purpose of evasion; and that I will well and faithfully discharge the duties of the office on which I am about to enter: So help me God.”

Notice what is not in there: The oath says nothing about supporting the president of the United States. It is silent about the Republican and Democratic parties. It does not mention the party leadership in the House or the Senate. It does not even mention constituents.

It does, however, insist that legislators bear allegiance to the Constitution, which at its core provides for a Congress that is an equal and independent branch of the government. In other words, it imposes the obligation on Members of Congress to act in ways that safeguard their institution’s place at the center of our representative democracy.

I wager that if you asked all 535 Members of Congress what that means in practice, you’d get 535 different answers. But surely it does not mean placing the interests of other institutions — whether it’s the presidency or powerful financial interests — first. At a minimum, I believe, it means giving one’s constituents and the country at large the benefit of independent judgment about how best to support and defend the Constitution. Weigh the various interests at stake, but think and act for yourself.

I don’t want to pretend this is easy. It’s in the nature of a lawmaker’s job that everyone from the party leadership to the White House to major campaign contributors expects — even demands — loyalty. “He’s not a team player” is not a compliment on Capitol Hill.

But I can also say from experience that when the day arrives for Members of Congress to walk away from the job — whether they be Senators or Representatives, Republicans or Democrats — they are not proudest of the times they rubber-stamped the president’s agenda or bowed to the wishes of the leadership. They’re proudest of the times they stood up for something they believed was right and insisted on their position even as their friends and colleagues pressured them to fall in line. These are tough, even agonizing, moments. But that’s what it means to live up to your oath of office.

Former Rep. Lee Hamilton (D-Ind.) is director of the Center on Congress at Indiana University and serves as director of the Woodrow Wilson International Center for Scholars.