For many Republicans, a cliff dive means blaming President Barack Obama for a big tax hike in the short term and then voting to cut taxes for most Americans next month. That’s an easier sell back home in Republican-heavy districts than a pre-cliff deal that raises taxes on folks making over $250,000 or $400,000, extends unemployment benefits and does little if anything to curb entitlement spending. If they back a bad deal now, they run the risk of facing primary challenges in two years.

For Democrats, the cliff is better than setting a rich man’s cutoff in the million-dollar range — or worse yet, extending the Bush tax cuts for all earners — and slashing Medicare and Social Security to appease Republicans. They, too, see an advantage in negotiating with Republicans who will feel freed from their promise not to vote to raise taxes once the rates have already gone up.

Plus, Obama’s polling in the mid-50s on his handling of the fiscal cliff situation, according to Gallup. Republicans are mired in the 20s. Why cave to the GOP when the president is winning?

In this way, what seems like the height of irresponsibility can be explained rationally.