I have gone over Chief Justice John Roberts’ majority opinion in today’s Voting Rights Act decision twice, and each time it has persuaded me that the V.R.A. should be revised in light of current conditions without persuading me that this is a question that the Supreme Court should be adjudicating. But rather than rehearsing my frequent complaints about how conservative judges have grown overly comfortable with their own style of counter-majoritarian activism, I’ll just express my agreement with Ramesh Ponnuru’s take on both the V.R.A. case and the looming gay marriage decisions, which he published before today’s ruling was handed down:We can ask a two-part question … that serves as a rough-and-ready guide to when the court should impose a policy. Did the people, by ratifying the Constitution or an amendment, mean to adopt that policy? Or did they mean to give the courts the power to force the adoption of the policy? If the answer to both questions is no, there should be a strong presumption against judicial intervention.

Nobody thinks the public meant to recognize same-sex marriage by ratifying the 14th Amendment, or to give judges the power to settle the issue. It’s the same with voting rights. The 15th Amendment gives Congress the power to enforce the right to vote “by appropriate legislation.” Conservatives say some parts of the Voting Rights Act are no longer appropriate. But nobody has offered any evidence that the ratifying public meant that courts should second-guess what Congress found appropriate.

Any defensible account of the proper role of the judiciary has to distinguish between what a conscientious judge does and what a conscientious legislator does, with the latter having the scope to take a wider range of considerations into account when weighing a law. In both the voting-rights and the marriage case, though, there is a temptation to erase that difference. A court that tries to determine whether all the provisions of the Voting Rights Act are “appropriate” to today’s circumstances is simply replicating the lawmaker’s task.

Yet that seems to be precisely what the Roberts Court did today. The decision’s argument for amending the V.R.A. is perfectly lucid, but it’s just that: An argument for updating a successful law to reflect contemporary realities, which under our system is supposed to be the role of the legislature rather than the courts.

And here it’s worth keeping in mind that a Republican-controlled Congress showed absolutely no interest in fulfilling that obligation when the V.R.A. was actually up for legislative review in 2006. On one level, that year’s 98-0 Senate vote, which extended the act by another quarter century, makes the case for judicial deference on the issue even stronger, since it suggests that a broad democratic consensus exists in support of the existing provisions. On another level, though, it’s an example of how Congress can effectively invite the judicial usurpation of politics, because that’s what many of the Republicans who voted to reauthorize the V.R.A. in 2006 were kind-of sort-of doing: They favored revisions to the act, but saw no political percentage in picking a fight on such a highly-charged, historically-freighted issue when it could be litigated through the courts at a lower political cost instead. So the Court’s intervention here isn’t just an example of judicial activism; it’s an example of judicial activism in a sphere where many members of Congress clearly preferred such activism to the exercise of their own constitutional prerogatives.

In a post today, Ezra Klein pins such congressional abdications on polarization and divided government: “During periods of gridlock,” he writes, “Congress cedes power to other branches that would otherwise give it deference.” But I think the phenomenon is characteristic of our entire era, and not just the last few gridlocked years. Our presidents have claimed broad and ever-expanding national security powers not in the teeth of congressional opposition, but with tacit congressional assent — because Congress would rather not have to take responsibility for anything as fraught as a declaration of war, let alone whatever the N.S.A. is getting up to. Our courts have taken on an outsize role in debates over race and sex, religion and culture, because those are issues that most politicians are extremely uneasy tackling, debating, and voting on. Regulatory expansions (like today’s climate change proposals from the president) are embraced by liberal politicians as an appealing alternative to casting controversial votes for tax increases in the same spirit that pro-business judicial activism is embraced by conservatives as an alternative to casting controversial pro-business votes.

In some of these cases, Congress is ceding power out of incapacity, but just as often it’s ceding it by choice — deferring to the imperial presidency, welcoming the encroachments of the administrative state, looking to the juristocracy for refuge and support on difficult and polarizing issues. So while it’s worth criticizing judges for their immodesty and our presidents for their power grabs, it’s also important to recognize the role played by legislators whose abdications have enabled both: Politics abhors a vacuum, and our elected representatives are often far to happy to have someone else step in and fill it — as five justices did today, and may well do again tomorrow.