Welcome to the period of “institutional flip-flops” — sudden abandonment of seemingly firm institutional principles, prompted by just one thing: the political party of the current president.

A few months ago, many Republicans were enamoured with an eight-member Supreme Court, an idea that Democrats treated as a constitutional atrocity. Now that a Republican is about to become president, prominent Democrats have no problem with a short-handed court, while Republicans treat the very thought as an outrage.

Under President Barack Obama, Republicans solemnly insisted on the importance of careful scrutiny of executive branch nominations, and they frequently resorted to the filibuster; Democrats argued for deference to the president and prompt confirmation of his choices. With the prospect of president Trump, Democrats have abruptly started to use some of the Republicans’ arguments, which they despised for eight years — while Republicans are sounding just like Democrats did.

Under President Obama, Republicans complained endlessly about White House “tsars”, in the form of White House officials who would oversee federal policymaking but who lacked Senate confirmation. Trump’s selection of similar “tsars” has produced not one peep of concern from Republicans — and if Democrats have not yet objected, well, just wait.

Institutions that Republicans used to love, like the Central Intelligence Agency, are now defended most vocally by Democrats. We’re bound to see much more of this, above all in sudden Republican receptivity to bold uses of executive authority (and with Democrats now insisting on the need to go to Congress first).

The lesson is clear and a bit sad: most politicians from both parties are only weakly committed to most of the institutional claims that they venture. In general, they really care about just one thing: outcomes. The appropriate role of the Senate in confirming presidential nominees raises complex questions, which are tough to answer in the abstract. It’s tempting to resolve them by asking a much simpler question: is the president a member of the political party I like? Institutional arguments are a smokescreen.

To be sure, institutional flip-flops are nothing new. They occur whenever a president of one party is followed by a president of another. But for two reasons, they are likely to be particularly troublesome, and potentially even dangerous, in the coming years.

The first reason is that the House, the Senate and the White House are about to be controlled by the same party (and, in all likelihood, the Supreme Court, which does its own flip-flopping, will soon be controlled by Republican appointees as well). When Republican candidates thought that Hillary Clinton would win, they told voters that a Republican-led Congress was necessary to impose a brake on her authority. That was a pretty good argument, at least if you are worried about the risk of presidential overreaching in the presence of a supine legislature. The second reason is that President-elect Trump has given strong signals that he is distinctly unenthusiastic about institutional norms that might constrain him (such as the idea of “one president at a time”).

Most of these norms have been established by longstanding practices; they cannot be found in the Constitution. As we live it, the system of the separation of powers depends largely on those norms, which establish a measure of forbearance and restraint.

Even if Presidents George W. Bush and Obama were not shy about using executive authority, they did not attack those norms. They never used the awesome power of the president to target their political opponents. Equally important, they embraced the idea that, in general, the president is allowed to act only if Congress has authorised him to do so — whether the issue involves the use of military force, homeland security, greenhouse gas emissions, civil liberties or immigration. Even when Bush and Obama acted aggressively, they usually avoided big claims about the president’s authority to act entirely on his own.

One reason was their own commitment to institutional limits on the president’s power. But both were probably influenced, at least once in a while, by a belief that Congress and the public would insist on those limits — and if they went too far, they would face serious opposition not only from the opposing party, but from their own as well.

Sure, institutional flip-flops are pervasive. But on the importance of respecting political opponents, and on the need for some kind of congressional authorisation for presidential action, people just haven’t flipped.

At least not yet.

• Cass R. Sunstein is a Bloomberg View columnist. He is the author of “The World According to Star Wars” and a coauthor of “Nudge: Improving Decisions About Health, Wealth and Happiness.”