BY AMBER PHILLIPS

We've called it "far-fetched." So have Republicans and, quietly, plenty of Democrats. And it still is by no means a given.

But with Donald Trump collapsing in key polls -- in a new Monmouth University poll, he's down by 9 points in Florida, a state he very much needs to win -- we're mapping out scenarios about how Democrats could retake the House of Representatives, and we're kinda surprised to be finding them plausible. Which all suggests just how bad this election could be for Republicans.

Republicans, we remind you, have the largest majority since before World War II, thanks in part to gerrymandered districts in their favor, self-sorting voters and the fact the president is a Democrat.

In 2016, Democrats need to net an extraordinary 30 seats to take back the majority. That means everything needs to go right for them in their six competitive seats AND they need to run the gamut in 27 Republican-held seats that nonpartisan analysts at Cook Political Report rank as competitive.

Here's why they could do it: Donald Trump is losing

And if he loses to Hillary Clinton by a big enough margin in November, it will be very hard for those 27 House Republicans to outrun him in their own races by a big enough margin. GOP pollster Robert Blizzard drove that point home in a tweetstorm Tuesday. The key tweet:

"Voters tend not to differentiate all that much," writes The Fix's Chris Cillizza, elaborating on Blizzard's point. "If they are voting against the Republican at the top of the ticket, they usually do the same down-ballot. It's why political waves occur — and why we call them waves."

But this wave is by no means a guarantee for Democrats

Three quick counterpoints from The Fix's Aaron Blake:

1. Democrats need to go into very rough territory — rougher than the GOP did in 2014: Some analysts have pinged districts like Rep. Kevin Yoder's in Kansas, which went for Mitt Romney by 10 points in 2012.

2. Democrats can't afford setbacks, but setbacks happen: We've already seen a few setbacks in potentially key races in Florida, Pennsylvania and a "zombie candidate" in Washington state.

3. Some Democratic candidates have very little money: "Part of the problem Democrats face," writes Blake, "is that Trump locked up the GOP nomination after it was too late to recruit in many states. That means Democrats are relying on some candidates that aren't top-tier or even second-tier recruits."

Still, if it's a wave election for Clinton, it might not matter who the candidate is or how much money they have. Bottom line -- and I can't believe I'm writing this -- The House majority is something to keep an eye on.

House Speaker Paul Ryan listens to House Minority Leader Nancy Pelosi in December. (AP Photo/Susan Walsh)

How do you measure President Obama's America?

(Illustrations by Thandiwe Tshabalala)

Exploring how his administration's policies affect our daily lives is one way to start. And the third installment of our series on Obama's legacy, out Tuesday, attempts to do just that by answering questions like: 

What if President Obama hadn't been able to pass a bill reforming our health care system? Would he have spent the final six years of his presidency mired in a series of high-stakes negotiations focused soley on keeping the federal government open?, asks The Post's Mike DeBonis.

(Illustrations by Thandiwe Tshabalala)

How did Obama make history with humor?  It wasn’t until Obama’s second term that he and his aides managed to fully harness the power of the digital media age, writes The Post's White House bureau chief, Juliet Eilperin. But he hit it out of the park with his interview with Zach Galifianakis on "Between Two Ferns" in 2013 that helped shift the narrative from a botched rollout of HealthCare.gov to, well, how funny Obama is.

The Post's video team went behind the scenes of that shoot. Fun fact: Obama had never heard of the show when he did it, and Galifianakis was really nervous when they started rolling.  

How did Obama handle the fastest moving social-change effort in these times, same-sex marriage? We get some answers in never-before-released footage from his phone call to congratulate James Obergefell, the plaintiff in the June 2015 Supreme Court decision that legalized same-sex marriage.  "Your leadership on this has changed the country," said the president, a man who, seven years earlier, had said "I believe marriage is between a man and a woman. I am not in favor of gay marriage."  

STAT OF THE DAY

14 points. That's how much support Trump lost for his idea to build a border wall among those who rated Trump unfavorably in December, writes Michael Tesler with Monkey Cage blog at The Post. Support for the wall has declined sharply among the American public overall, even though his supporters still tend to like it. Tesler says Trump's unpopularity among Americans is making his signature policy proposal unpopular, too. 

Side note: Over the past few decades, Congress has actually authorized hundreds of miles of fencing along the border. So if Trump were president with a Republican Congress, it's not hard to see them considering a wall. 

NEWS FROM THE TRAIL

Trump's campaign is denying a CNN report that ousted Fox CEO Roger Ailes is advising Trump. Trump's stiff arm of Ailes underscores how Ailes has gone from a major party power broker to a liability after women at Fox raised sexual allegations against him. “They are longtime friends, but he has no formal or informal role in the campaign,” Trump spokeswoman Hope Hicks said in a statement to the Post's Jose DelReal.  

Congress will review in secret documents from the FBI's conversations with Clinton about her emails. Getting to look at such extraordinarily sensitive documents is a win for Republicans who are upset at the FBI's decision not to prosecute Clinton for using a private email server. But as I've reported before, there's not much House Republicans can do to make the government prosecute her. Clinton's campaign told reporters Tuesday that she hoped her interview with the FBI would be made public. 

Pennsylvania's attorney general, Kathleen Kane, will resign after a jury found her guilty of leaking secret grand jury information and lying about it. The case is as complicated as it is fascinating -- the saga begins with pornographic emails and ends with a rising star becoming a convicted criminal. I have an explainer here.  

Donald Trump is still spending less on TV than ads than Jill Stein, reports The Fix's Philip Bump. In fact, Clinton spent more on advertising in June than Trump did on his entire campaign for May, June and half of April. Which raises the question yet again: When is he going to start campaigning?  

(Philip Bump / The Washington Post)

Even in a swing state where Clinton has a strong lead over Trump, Democratic candidates don't always feel comfortable talking about her. New Hampshire Gov. Maggie Hassan, who is challenging Sen. Kelly Ayotte (R) in a race that could determine which party controls the Senate, was asked three times by CNN's Manu Raju whether she thinks Clinton is honest. Three times, she dodges.

THE VIEW FROM THE TRAIL

Trump headed to Wisconsin:

Trump surrogate update #1:

Trump surrogate update #2:

Serbian Radical Party leader Vojislav Seselj and his party members protesting in front of the Serbian Parliament building against the visit of Vice President Joe Biden in Belgrade Tuesday. / AFP PHOTO / ALEXA STANKOVICALEXA STANKOVIC/AFP/Getty Images

YOUR DAILY TRAIL PIT STOP: #SCIENCE Both Trump and Clinton are underwater right now. So is this "impossibly cute" squid. Since you've probably heard from both candidates already today, take a moment to meet Rossia pacifica, more commonly known as the stubby squid.