The departure of Montana Gov. Steve Bullock over the weekend from the presidential campaign makes it official: governors are no longer considered viable candidates for the presidency while senators – once dismissed as weak competitors – have dominated the pre-primary season.

The whittling down of the massive Democratic presidential field, particularly the early exodus of the three governors in the lineup, surely confirms that a sea change has occurred in the way that we choose a president.

Consider this: All but one of America’s presidents between 1976 and 2008 were governors. George H.W. Bush was the outlier.

Since that 32-year stretch, the 2008 general election featured John McCain vs. Barack Obama – the first time since 1856 that two senators had squared off for the White House. Obama prevailed and in 2012 he comfortably defeated former Gov. Mitt Romney. And in 2016, 11 (current and former) governors ran and lost, with nearly all dropping out early in the election season.

This year, Bullock joined former Gov. John Hickenlooper of Colorado and former Washington Gov. Jay Inslee in failing miserably at gaining traction in the wide open presidential race on the Democratic side. Instead, Sens. Elizabeth Warren and Bernie Sanders have emerged as the clear challengers to former vice president (and former senator) Joe Biden.

Senators still in the mix include Amy Klobuchar, Cory Booker and Michael Bennet.  Sen. Kamala Harris exited the race today after she had briefly secured a position months ago as one of the early frontrunners.

For decades, both parties’ primary voters expressed an undeniable preference for governors who had “the buck stops here” executive experience as opposed to senators, who were sometimes viewed as “blowhards” who rarely had to make a decision that entailed inescapable consequences.

In fact, through much of post-Civil War history governors have regularly won their party’s presidential nomination – and often the White House — while the Senate was viewed as a political graveyard for presidential candidates.

That tradition returned after Watergate when an obscure governor from Georgia, Jimmy Carter, was elected over Gerald Ford, as the nation sought a clean slate. Ronald Reagan, a former governor of California, was next to be elected in 1980.

In 1988, Massachusetts Gov. Michael Dukakis was nominated by the Democrats and, at one point, held a huge lead over Vice President George H.W. Bush late in that campaign. Dukakis had won the primaries in part by defeating four senators.

Four years later, the little-known governor of Arkansas, Bill Clinton, made an improbable run for the Democratic Party nomination and ended up in the White House. In 1996, he easily defeated the Republican Senate leader Bob Dole for re-election.

In 2000, Texas Gov. George W. Bush scored a miniscule Electoral College win over Clinton’s VP, former senator Al Gore. Bush defeated former Sen. John Kerry for re-election four years later.

In the current race for the White House, none of the big-state Democratic governors took a crack at a presidential run. In a year when left-leaning Democratic primary voters yearn for big-government solutions, their distaste for Republicans seems to have reached a new level. As the 2020 primaries approach, their view is that moderate governors need not apply.

Hickenlooper’s prime selling point was his governing accomplishments while dealing with a Republican legislature. Similarly, Bullock had billed himself as a pragmatic leader who has succeeded in a deep Red State that voted overwhelmingly for Trump in 2016. Inslee ran as a one-issue candidate, with climate change as his priority.

One expert told Governing.com that the pragmatism and executive experience that governors emphasize on the presidential campaign trail is now brushed aside by fired-up partisans:

“Being a governor ain’t what it used to be in running for the White House,” says Saladin Ambar, author of How Governors Built the Modern American Presidency.

Historically, Ambar notes, governors fared well in national politics when voters were fed up with Washington. Yet the public’s trust in the federal government is near an all-time low, and governors are still failing to gain any traction.

“In choosing Trump, Americans went for the ultimate outsider, someone with zero government experience,” says Ambar, a political scientist at Rutgers University. “Governors’ shtick, if you will, has been usurped.”