This election year has repeatedly broken the mold, and while cross-party support has precedent, its volume this year is extraordinary. Just look at Hillary Clinton. She approaches the fall with an impressive collection of Republican allies—candidates, elected officials, and opinion leaders—who have landed in her corner.

Until this summer, Republicans who objected to Donald Trump clung to the hope that his nomination would be thwarted, keeping the disavowals at bay. Now, the environment is different. The seal is broken, with a critical mass of prominent Republicans having spoken out against the nominee, while polling evidence mounts that the ticket is floundering. Clinton leads Trump by an average of 6 percentage points in the 10 most recent post-convention polls.

Some arrive to Clinton’s side only through binary logic, positing that failure to support Trump is the same as supporting Clinton. George H.W. Bush and George W. Bush’s silence puts them in this camp, along with others voicing a deliberate “no.” To name a few: former senior advisor and deputy chief of staff during the George W. Bush administration, Karl Rove; conservative columnist George Will, who left the Republican Party; and the as-good-as-no Sen. Ted Cruz (R–Texas).

Others directly align with the Democratic nominee, either through their vote intent or formal endorsement. The recent stretch has been good for Clinton in this regard, with high-power movers from past Republican administrations coming over—former national security assistant under presidents Gerald Ford and George H. W. Bush, Brent Scowcroft; former CIA acting-director Mike Morell; Paulson Institute chairman and former U.S. treasury secretary and chief executive of Goldman Sachs (GS), Hank Paulson.

History is peppered with elections marked by cross-party support. Breaking ranks with their party in 1896, free-silver Republicans stood with the Democratic nominee, populist William Jennings Bryan, who appealed to Trump-like anxiety, though with more rhetorical prowess. The year 1964 offers the best analogy, with a polarizing, ideological Sen. Barry Goldwater (R–Ariz.) as nominee, prompting Republicans to cross party lines. Their disaffection was not lost on President Lyndon B. Johnson, who attempted to lure Republicans to his side.

At this juncture in 2016, defectors to Clinton make up a small fraction of the Republican elite, despite the steady clip heading to the off-ramp. Still, their numbers exceed those from other contests, and their significance surpasses mere numerical strength. Most Republicans supporting Clinton subvert the very message that Trump needs to sell: that he is fit to lead the country.

The departures reached fever pitch in the week following the Democratic Convention, with Trump repeatedly stumbling and compulsively attacking the Gold Star family of Capt. Humayun Khan. At about the same time, Clinton picked up her first full endorsement from a sitting Republican member of congress, U.S. Rep. Richard Hanna (R–NY), and strong support from president and CEO of Hewlett Packard (HPQ) Meg Whitman, who also urged fellow partisans to follow suit.

President Barack Obama caught the wave as well, calling on Republicans to abandon their nominee, and the Clinton campaign reportedly plans to actively recruit.

The phenomenon of Republicans disavowing their nominee took off in earnest with Trump’s June attacks on U.S. District Judge Gonzalo Curiel, then again with his post-nomination meltdown in his remarks about the Kahn family and the Second Amendment. But while Trump provides plenty of fodder for principled objections—his policies, expertise, and character—the timing of defections underscores that these are strategic decisions—calculations based on the interests of the defector. Even principle is pursued strategically.

At this point, vulnerable Republican candidates can picture themselves being dragged under, which makes cutting the tie more compelling. Even those electorally secure or not on the November ballot are at risk if Trump prevails and acts on his more extreme pledges. This campaign could cast a long shadow, trapping with blame disaffected Republicans who stay silent, but also empowering future opponents of those who jump ship, despite the growing security in numbers.

It remains, however, that even most of Trump detractors find the Democratic nominee anathema, with the immediate costs of actively supporting her far greater than any perceived benefit. After all, Republican voters still support their nominee, and even independents lean slightly toward Trump. The off-ramp offered to Republican leaders by Libertarian nominee Gary Johnson could sooth their conscience, but in all likelihood, does little to derail Clinton.

It may be that relying on voters to maintain partisan balance is the most promising route for many. Their pitch would be straightforward: With the prospect of Clinton in the White House, it’s critical to elect Republicans to Congress.

Suffice it to say that the strategic calculus for the GOP is complex, and certainly unique for each decision maker. That either Obama’s or Clinton’s open-door policy or their active recruitment of Republicans would register positively in the calculus is, however, highly unlikely. At this stage, they have small parts in the evolving Republican drama.