A more cautious army than the Democrats would have suspected a trap the moment Barr spurned the House Judiciary Committee. This veteran of Washington warfare easily shrugged off hours of questions from a Senate panel concerning special counsel Robert S. Mueller III and his lightly redacted report. Barr could have sparred for another day in the House just as comfortably and pugnaciously. Barr’s decision to boycott can only be understood as a deliberate provocation.

Instead of finding a way to avoid an ambush, Democrats have plunged ahead. The judiciary panel voted along partisan lines to hold Barr in contempt of Congress. Another fight is joined over access to Mueller’s trove of evidence. And the most determinedly self-destructive Democrats continue to push for impeachment.

This battle royal between the legislative and executive branches will grind its way through the courts — all the while allowing Trump to continue hogging the media’s attention. Meanwhile, some two dozen would-be Democratic nominees are starving for airtime. House Democrats could be passing popular legislation and forcing Team Trump to block it, thus laying the groundwork for the coming campaign. They appear trapped in their Trump obsession.