Part of the Republican Party’s weakness as an opposition party is structural. Republican politicians don’t care that much about solving problems through public policy because Republican voters don’t care that much, either: In a recent Echelon Insights poll, only 25 percent of Republicans said they believed the goal of politics is to enact good public policy; that number shrunk to 19 percent among the party’s most dedicated Trump supporters. Part of it is historical, an outgrowth of the party’s recent strategy of opposing Democratic plans without unifying around alternatives of their own. That generalized refusal to engage with policy trade-offs became endemic under Mr. Trump, whose shallow approach to so much economic policy made the already difficult work of developing and uniting around innovative policy ideas effectively impossible. It’s not that the party has no ideas at all. But there is little in the way of consensus on economic policy and how to improve it, even among those who are looking to forge new paths for the right: Notably, when Senator Mitt Romney of Utah introduced a proposal for a broad-based child allowance, he was attacked by Senator Marco Rubio of Florida — who had previously made waves by pushing to expand the child tax credit.