There is more than one way to demolish a wall, physical or legal. Go at it with a bulldozer, or weaken its foundations and await the collapse. When it comes to undermining the structure of modern campaign finance law, Chief Justice John Roberts has done it both ways.

The 2010 ruling in the Citizens United case, which Roberts joined, was a judicial bulldozer, willy-nilly toppling precedents that had restricted corporate spending on elections.

But the chief justice prefers a cannier jurisprudence, less in-your-face but perhaps just as destructive. Wednesday’s ruling in McCutcheon v. Federal Election Commission, invalidating limits on the overall amount of donations an individual can give to federal candidates and committees, illustrated that insidiously effective approach.

The risk posed by the ruling, in which the chief justice wrote the plurality opinion, is not as much its immediate impact but the implications of its reasoning in demolishing an already rickety campaign finance structure.

McCutcheon’s critics wail that it clears the way for wealthy individuals to plow millions into political campaigns. Um, but where have they been? The opportunities to write seven- and eight-figure checks were plentiful before the ruling. The difference that McCutcheon makes is that mega-donors have previously had to conduct their political spending indirectly, through super PACs or other entities that do not write checks straight to candidates or parties.

Pre-McCutcheon, such direct giving had been limited to $123,200 per election cycle. Now, motivated donors can write checks totaling $3.6 million to a party and its federal candidates. Actually, through the magic of a “joint fundraising committee,” donors need write only a single check.

The immediate repercussions are less than some overwrought critics claim. First, the four-justice plurality could have gone further, as Justice Clarence Thomas urged, dismantling the distinction between contributions and expenditures and tipping the scale against even contribution limits.

Second, caps on the size of checks to individual candidates remain in place. Ominous predictions notwithstanding, these limits strike me as safe even under the majority’s hostile approach.

Third, while big checks straight to candidates and parties are more corrupting than big checks spent on their behalf — ask politicians which they prefer — the consolation is that at least such donations must be disclosed, not hidden in the “dark money” crevices of the federal tax code.

In fact, to the extent that disclosure is the best remaining solution to Wild West campaign rules, Roberts’s opinion offers useful support. “With modern technology, disclosure now offers a particularly effective means of arming the voting public with information,” Roberts noted.

The real risk lies in the conservative justices’ seemingly deliberate obtuseness to the real world of campaign contributions — in particular, their cramped understanding of what constitutes the kind of corruption or risk thereof to justify campaign finance legislation.

The problem started with Citizens United, when Justice Anthony Kennedy looked at independent campaign spending and couldn’t imagine how it might corrupt candidates.

“In fact, there is only scant evidence that independent expenditures even ingratiate,” he scoffed. “Ingratiation and access, in any event, are not corruption.” The test for whether such spending corrupts, Kennedy said, is much stricter: whether it constitutes a quid pro quo of largesse for political favors.

Justice Kennedy, you might want to read about GOP politicians trooping to Las Vegas to woo mega-donor Sheldon Adelson.

In McCutcheon, Roberts oversaw the metastasis of Kennedy’s unrealistic test from expenditures to contributions. A politician receiving one humongous check, with proceeds to be distributed among candidates and party committees, will naturally be “grateful” to the donor but will not feel “obligated” in a way that constitutes corruption, he asserted, happily substituting his judgment about what is corrupting for that of members of Congress who might actually know.

Mr. Chief Justice, you might want to talk to lawmakers scrambling to collect enough cash to secure committee chairmanships or other plum assignments.

Where does this see-no-corruption approach end? In 2003, upholding the ban on soft money contributions to political parties, the court noted that such unlimited checks posed the threat of both “actual corruption” and “eroding . . . public confidence in the electoral process.” It’s hard to see the soft money ban surviving the new quid pro quo standard. Indeed, it’s hard to see any limits on party donations surviving: How exactly do parties provide a quo for the quid? Similarly imperiled: the ban on direct giving by corporations and labor unions.

The conservative bulldozer hums, awaiting the next opportunity for dismantling.

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