That, of course, reflected an era when now-extinct species like liberal Republicans and conservative Democrats gamboled on the Capitol lawn. But once the parties became ideologically cohesive and voters polarized, ticket-splitters became as rare as ample legroom in a coach seat.

 

In an oft-cited number from “Vital Statistics on Congress,” just 26 congressional districts rendered a split verdict in 2012 — veering in one direction for president and the other for the House. The pattern continued in 2014 with only 31 House districts deviating from their 2012 presidential choices.

 

Both parties embraced the prevailing orthodoxy that the only way to win congressional elections was to mobilize partisan supporters. Politics became a scare-a-thon testing which party did a better job at frightening voters into racing to the polls to avoid the purported apocalypse. 

 

“It’s been the working model for both sides because it’s a comfortable model,” says Republican pollster and strategist David Winston. “But, as a result, there has been almost no way for the parties to have an effective and positive dialogue with the voters.”

 

But now all bets are off.

 

“This is the oddest, most unpredictable election in modern history — or maybe ever in American history,” says G. Terry Madonna, a political historian and pollster at Franklin & Marshall College. “We’re in uncharted territory here.”

 

Only a few months ago, many political analysts (myself included) dismissed Donald Trump because he lacked establishment support and had collected only a handful of congressional endorsements. Political science orthodoxy, reflected in the 2008 book “The Party Decides,” dictated that maverick candidates invariably fell short in the quest for the presidency.

 

The danger here lies in getting wedded to a model. Though, on reflection, that may not be the best phrasing for a discussion of Trump.

 

Seriously, there is an irresistible temptation to believe that there are unalterable Iron Laws of politics. Take the frequently repeated assertion that it is almost impossible for the president’s party to win three consecutive terms in the White House. After all, since World War II, only George H.W. Bush in 1988 has defied the three-term curse.

 

It seems persuasive, even though Barack Obama’s approval rating is now edging over 50 percent. After all, the incumbent party lost in six of seven tries for a third term: 1952, 1960, 1968, 1976, 2000 and 2008. But, in truth, the evidence is muddy since Al Gore won the popular vote in 2000 and Richard Nixon may have edged John Kennedy in 1960, if you take away Chicago Mayor Richard Daley’s artful vote counting.

 

In similar fashion, split-ticket voting may not be dead — it may merely be sleeping.

 

Voters can still, when motivated, pick candidates from different parties. Montana Democratic Sen. Jon Tester held his seat in 2012 by running eight points ahead of the Democratic ticket. And about 15 percent of Ohio voters in 2010 opted for victorious Republican Sen. Rob Portman and losing Democratic incumbent Gov. Ted Strickland, according to exit polls. An intriguing 2016 question is how these Ohio ticket-splitters will vote in a Senate race pitting Strickland against Portman.

 

A major reason for a potential surge in 2016 voters who hopscotch down the ballot is that both political parties have lost ideological cohesiveness. Trump is offering voters the cult of personality rather than any coherent governing philosophy — or, in fact, any coherent anything. And Hillary Clinton has been stressing national security views that appeal to centrist Republicans more than Democratic doves.

 

The undeniable truth right now is that anyone who thinks that they can handicap the 2016 elections — both for the White House and Congress — is wrong. We are drowning in evidence (polls, political precedents, pundit proclamations), but there is no reliable way to decipher the clues.

 

When Trump is talking about contesting true-blue Connecticut and Clinton somehow believes that Texas can be competitive, the only smart-money play is to keep the cash in your wallet.

 

With the two presidential contenders wildly unpopular (though nobody can trump Trump), smart congressional candidates in both parties should prepare themselves for what may turn out to be a split-ticket year that feels ever so 20th century.