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Donald Trump’s bad month just got worse, because Sanders backers just rallied to Clinton

Hillary Clinton and Bernie Sanders before the CNN Democratic presidential debate on April 14, 2016, in New York. (Jewel Samad/AFP via Getty Images)

Donald Trump would like for Bernie Sanders supporters to ditch the Democratic Party and support him. There is very little evidence that they will do that, mind you, but it's certainly possible that they might just stay home — which would help Trump.

Well, we have some bad news for the Trump campaign. Sanders supporters aren't just rallying around Clinton; they're doing it rather quickly. And it's a big reason Clinton just extended her lead over Trump into the double digits, 51 percent to 39 percent.

A new Washington Post-ABC News poll shows that Sanders backers, who polls have shown were reluctant to jump over to Clinton and even flirted with supporting Trump, are coming home faster than we might have expected.

VIDEO: Watch Clinton and Trump try to woo Sanders voters after June 7 primaries

Last month, 20 percent of Sanders supporters said they would back Trump over Clinton in the general election. This month, that figure is down to 8 percent.

And the poll was conducted before, we would note, Sanders began saying last week that he would support Clinton over Trump in the general election. (Even as he's not endorsing Clinton and is still technically a candidate, Sanders said his supporters would and should not vote for a "bigot" like Trump.)

When asked on MSNBC June 24 if he would vote for rival Hillary Clinton, Democratic presidential candidate Bernie Sanders answers, "Yes." (Video: Reuters)

In a way, this was expected. Clinton backers in 2008, after all, eventually came around to Barack Obama's candidacy and overwhelmingly supported him in the general election. We've used this as our baseline in comparing how quickly Sanders supporters might come around to Clinton in 2016.

But here's the thing: It took them a while. In June 2008, 20 percent of Clinton backers said they'd go for John McCain. In July, it was 22 percent, then 18 percent in August and 19 percent in September. It finally dropped to 14 percent in October.

Well, it's June 2016, and that same figure this time is down to 8 percent already. What's more, the 81 percent of Sanders backers who are now behind Clinton is a higher number than in any poll of 2008 Clinton backers who rallied to Obama. The high that year was 74 percent, in October.

And, really, the idea that Clinton backers would cross over for McCain was probably more plausible in the first place. She was the more moderate candidate in the Democratic primary, so it wasn't unreasonable to think that her more moderate supporters might go for a moderate Republican such as McCain.

Sanders was decidedly not the moderate option in the 2016 Democratic primary. He does share some populist tendencies with Trump — which Trump has tried to leverage to get Sanders supporters to join him — but it was always a somewhat fanciful effort by Trump to woo them.

Indeed, as a Pew poll last week showed, Sanders supporters were more anti-Republican Party than Clinton backers. About 7 in 10 of them, in fact, said the Republican Party makes them "afraid" — vs. 55 percent of Clinton supporters.

That was never really a recipe for a big crossover vote. And this poll suggests that possibility has been foreclosed.