So why isn’t Clinton following Nixon’s example? For reasons as clear-eyed as her takedowns of Obama. First, she is in a stronger position to win her party’s nomination today than Nixon was 48 years ago.

Second, she, unlike Nixon in 1966 and like most sober-minded observers this year, doesn’t see this as a good year for her party.

One reason is structural. The Senate seats up for grabs this year are in states that, on average, voted 52 percent for Romney and 46 percent for Obama in 2012. Obama won by an average of only 50.1 percent in seats now held by Democrats and received only 39 percent of the vote in states with seats held by Republicans.