The GOP's months-long effort to paint Biden as doddering and senile backfired massively with his solid DNC speech

Soaring oratory has never been Joe Biden's strong suit.

But going into the biggest speech of Biden's almost five decades in national politics, the Trump campaign and the GOP made a concerted effort to paint the Democratic nominee as doddering and in "cognitive decline," lowering expectations.

The Trump campaign even secured the pricey and highly influential ad space of YouTube's top banner on Tuesday to show an ad painting Biden as senile, juxtaposing old clips of the vice president with others of him stuttering or losing his train of thought on the 2020 campaign trail.

President Donald Trump's adult sons, Eric and Donald Jr., appeared on Fox News all week claiming that Biden couldn't even string a sentence together.

The bar was set so low for Biden going into his address at the Democratic National Convention on Thursday that a merely competent performance would have helped the campaign.

But after two failed bids for the presidency in 1988 and 2008 — along with being on the ropes in the 2020 primary before South Carolina — Biden not only made sure he wouldn't squander the opportunity with any slip-ups but brought his A-game, teed up by the cognitive-decline attacks to "hit a home run in the bottom of the ninth," in the words of the Fox News anchor Dana Perino.

Biden managed the rare feat of earning praise from multiple Fox News panelists following his speech.

Without the relentless attacks on Biden's mental acuity, such an overperformance would have been much harder to imagine.

As long as Trump keeps insisting that Biden "can't put two sentences together," this dynamic could prevail through the rest of the campaign, particularly in the debates.

A casual viewing of the Democratic primary debates should have indicated that Biden is the biggest beneficiary of assumptions that he's lost a step with old age, much less that he's senile.

If that wasn't enough of a reason for Republicans to think twice about going after Biden's mental faculties, his strong polling among older Americans should be.

Claiming, without evidence, that someone who's 77 years old can't even read from a teleprompter opens up a 74-year-old Trump and his obsession with a dementia-screening test to easy counterarguments of hypocrisy and risks offending one of the most reliable and sought-after voting demographics.

The Biden campaign also prefaced the speech with a tribute video from 13-year-old Brayden Harrington of New Hampshire, who spoke about how Biden connected with him on the campaign trail over his stutter and told him they were "members of the same club."

For all the Trump campaign's hemming and hawing over Biden hiding in his basement, the months of cognitive-decline attacks only helped the Democrat's campaign.

By setting the bar this low, the Trump campaign's "Sleepy Joe" strategy backfired, leaving a gift at the top of the basement steps for the grandfather of six.