AMERICA has been pretty much stuck in neutral for the past few years, as Republicans used their gains in the 2010 elections to prevent Barack Obama from pushing any of the major items on his agenda through Congress. Mr Obama's jobs bill, climate-change legislation, gun-control initiatives, immigration reform, and even many of his appointments to executive posts have been stymied. Republicans in the House, rather than pass legislation that Senate Democrats might conceivably negotiate over and ultimately approve, have largely concentrated on confrontational symbolic gestures, such as bills repealing Obamacare. This has been an effective political strategy for Republicans, who have watched the president's popularity steadily decline. They will likely gain a lot of seats in this autumn's elections. But given that the block-everything congressional strategy works so well to undermine a president, and provided that the Senate's filibuster rules continue to require a 60-to-40 majority to get anything passed, will America's government ever pass any significant laws again? Is permanent gridlock the logical end-state of the system? The guys behind the liberal Democratic website Primary Colors released an interesting graph this week suggesting that all is not lost—though not, perhaps, in the way that liberal Democrats might hope. The idea behind Primary Colors is to identify the prospects of more extreme Democratic legislators in primary elections, and measure how this might affect the party in November, when more moderate politicians may have a better chance of winning. Primary Colors uses an algorithm that compares Democratic legislators' voting habits to the ideological complexion of the district they represent, in order to pick out congresspeople who vote significantly to the right of their constituents. The idea is to replace them with more leftist candidates who can still get elected.

But the algorithm, the website points out, also shows something else. The reason it's a useful tool is that the voting behaviour of Democratic representatives does in fact vary according to the partisan leanings of their districts. Democrats in more conservative districts generally vote more conservatively. When you apply the same algorithm to Republicans, it becomes clear that they don't behave the same way: