Donald Trump's campaign is collapsing before our very eyes. Unable to be anything but his erratic self, the Republican presidential nominee is down by double-digits to Hillary Clinton in some polls. Instead of talking about what he would do as president or attacking his rival, he keeps lashing out at every perceived barb. Everyone around him is suddenly realizing that he just can't help himself, and is riding the Titanic full steam ahead into the iceberg.

It's hard not to think of an alternative, a sort of bizarro nominee. Someone who is disciplined, not erratic. Compassionate, not vengeful. Knowledgeable, not ignorant. Inclusive, not divisive. It's hard not to consider how Marco Rubio would be doing atop the ticket.

Wait! It's not that crazy. An article by Vox's Dylan Matthews envisages a scenario where Rubio is the nominee because Trump finally decides not to run. But it's quite possible to imagine that Rubio could have won even with Trump in the race — say by not royally screwing up the New Hampshire debate, winning South Carolina, and later solidifying the non-Cruz, non-Trump vote.

So let's talk through this parallel election.

First off, the Republican Party and its presidential nominee would be in a very different position out of the gate. After all, the party has its largest majority in Congress since 1929. It controls most states. And the Democratic Party has decided to nominate the most disliked presidential candidate in modern history (besides you know who) and the living embodiment of the Washington establishment in an anti-establishment year.

In this scenario, the story about the Republican convention wouldn't have been about the party's apocalyptic visions or disunity — it would have been about the inspiring personal story of Rubio's immigrant parents, his student loans, and his belief that wage subsidies and child tax credits can help families like his parents'. Meanwhile, without a dumpster fire on the other side to contrast with, the main story about the Democratic convention would have been Bernie Sanders' holdouts and how far Hillary Clinton had to veer to the left to satisfy his supporters (who still aren't satisfied).

The RNC, raising more money than any campaign committee any cycle, would be relentlessly hitting Hillary over her countless scandals and flip-flops and successfully defining her as a grifter — payback for what the Obama campaign did to Mitt Romney in the summer of 2012.

And with the wave of terrorist attacks in Europe, the Republican nominee could have talked up his calls from the Senate to strengthen border security and to pay more attention to the rise of ISIS when it could have been stopped — instead of, say, making people wonder if he wouldn't nuke a place just because he feels like it.

Clinton's necessary strategy of mobilizing minorities to vote against the Republican standard-bearer, already tricky given his personality, would have been blunted with a Latino speaking about inclusivity at the top of the ticket.

All of sudden, Clinton's path to victory begins to narrow. Rubio's home state of Florida would be looking particularly good for Republicans, as would Virginia with its coalition of upscale suburban voters and rural conservatives.

And the Republican nominee would have — dear Lord almighty — message discipline. He would have talked about issues that matter to most Americans.

If all this were true, the Republican nominee would be up in the polls by much more than the margin of error. He'd probably even stay there throughout the race — and maybe even rise further, barring some software glitch, after the debates.

Why do I say this? Not just to indulge in a fantasy. But to point out to everyone at the Republican Party who enabled Donald Trump that which they already know: You did this to yourselves. You have nobody to blame but yourselves.