FOR THE most part, Tuesday’s opening session of the 115th Congress was about pomp and circumstance. Still, the prepared speeches and swearing-in ceremonies reminded everyone that — for all the ferment over an impending Donald Trump presidency — there is also a legislative branch of government in the United States. Republicans control the Senate and the House as well as the presidency and are all but salivating over the power to enact dramatic changes to the course President Obama charted during the past eight years. But some wiser GOP leaders are at least questioning whether exploiting their majority to maximum effect would be good for the country or, for that matter, the party.

Of course, on the merits we oppose some GOP plans, such as repealing Obamacare and replacing it with — what? It could take months of grueling legislative combat to answer that question; but we fear it could involve curtailment of the Medicaid expansion that accounted for most of Obamacare’s improvement in overall insurance coverage. The Republicans also have the votes to populate federal agencies and the Supreme Court with Mr. Trump’s picks, many of whom already strike us as doubtfully suited to their new positions.

Still, there’s no denying that the Republicans won in November and that they therefore have the right to enact as much of their agenda as they lawfully can. In his first speech as Senate minority leader, Charles E. Schumer (D-N.Y.) gamely promised to exercise vigilance over Mr. Trump and to “resist” him when Democrats believe he has veered into extremism. Yet even with the power to filibuster ordinary legislation and Supreme Court picks, the minority party has limits to how much defense it can productively play. In some instances, Mr. Schumer may do better by standing aside and letting Republicans fight among themselves. Unexpected victory has helped the party sublimate its factional quarrels and the misgivings many still have about Mr. Trump, but those are bound to flare up again.

Republicans have an opportunity for a more positive form of self-restraint, however. GOP Senate leaders have pointedly reminded Democrats of how Mr. Obama’s party exploited its temporary control over Congress and the White House to enact his agenda in 2009, noting that voters have been electing Republicans to undo it ever since. That history could just as well be construed as a reason for Republicans not to commit the same mistake in the opposite direction.

They’d certainly be smart to view it that way. Senate Majority Leader Mitch McConnell (R-Ky.) is the author of the resistance strategy that helped the GOP thwart many of Mr. Obama’s plans; it would be naive to take his calls for comity and institutional stability at face value now. Since the election, however, Mr. McConnell has stood out among Republicans for his warnings against overreach. “It’s certainly no time for hubris, because all majorities are never permanent,” he said on a Kentucky television program last month. Discussing the 2017 Senate agenda, he has played down more polarizing issues such as immigration in favor of potentially bipartisan ones such as tax and regulatory reform. If the GOP Congress is willing to proceed with caution, Democrats should be willing to respond in good faith.