John Oliver provides a step-by-step takedown of Donald Trump's 'serious' Mexican wall proposal

Possibly the first specific plan Donald Trump presented during his presidential run was a wall between Mexico and the United States.

The Republican frontrunner proposed the wall after his controversial statements about Mexican immigrants during the announcement of his presidential run. And since it has stuck, "Last Week Tonight" host John Oliver decided to take a close look at the proposal on Sunday's episode.

"The border wall is one of the few policy proposals that Trump has talked about in detail," Oliver said. "So instead of mocking or dismissing it out of hand, tonight let's take a serious proposal from a serious presidential candidate seriously."

The host promised to put aside the "potential racism and xenophobia" of the proposal. "We can come back to that later," he added, before jumping into the cost of Trump's border wall.

Made out of concrete, rebar, and steel, the 32-foot, 1,000-mile-long wall would cost $12 billion on the high end, according to the real-estate mogul. Oliver said that experts estimate it would actually cost about $25 billion to build.

But here's the kicker: Maintaining the wall is estimated to exceed the cost of building it within seven years.

"So it's a big dumb thing that only gets more expensive over time," Oliver pointed out. "It's like getting a pet walrus. You think it's stupid now, wait until you learn what a bucket of sea cucumbers costs. You've not prepared for that."

But wait, hasn't Trump said many times that Mexico will pay for the wall? According to the country's treasury secretary, and two former presidents, Mexico isn't sending the US a check for the border wall.

Trump has suggested that the wall would be paid for because of the $58 billion trade deficit the US has with Mexico, but Oliver explains that that's not the government's money to spend.

"[The money] is not lying around in some centralized Scrooge McDuck money bin labeled, 'Dumb Americans' money. Do not spend on border fence,'" Oliver pointed out.

So Oliver says the wall just isn't going to happen. But he's thorough, looking at where the wall could be built and discovering a few more reasons it would be impossible.

And beyond that, Oliver decided to pretend as if the wall could get built. Will it even work to keep immigrants and drugs cartels out of the US? According to him, no.

But the host has his own outrageous proposal.

Watch Oliver demolish Trump's big wall proposal and present his own below:

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