A huge mistake by the GOP has opened the door for Biden to dominate the first debate and take a commanding hold on the election

• The GOP has for months been trying to make it seem as if Joe Biden is in cognitive decline.
• Biden has the chance to easily refute this incorrect theory during the debate on Tuesday.
• By sticking to a short, strong message Biden can easily overwhelm President Donald Trump and cement his lead in the presidential election.
• Michael Gordon is a longtime Democratic strategist, a former spokesman for the Justice Department, and the principal for the strategic-communications firm Group Gordon.
• This is an opinion column. The thoughts expressed are those of the author.
• Visit Business Insider's homepage for more stories.

As Joe Biden began to emerge as the Democratic presidential nominee, Republicans and conservative commentators developed a strategy to undermine the former vice president with a claim that he is in cognitive decline. 

They seized on random gaffes. They made fun of his stutter. They labeled him "Sleepy Joe." All the while, the GOP standard-bearer was wondering if Americans should inject Lysol. 

Then, as debate season approached, Republicans realized that they needed to do a 180. By setting the bar for Biden's cognitive abilities so low, it will be easy for the Democratic nominee to jump over it and defy "expectations."

The sudden need for a new game plan is not the first time this month that Republicans have needed to dramatically shift course. But it's too late for their zig zags to work after months of hammering home the "Biden cognitive decline" message. They've set it up so that all he has to do is show up, and he'll shine.

Indeed, if the former VP plays the debates right, he will close the deal with the American people. Here's how he can do it.

Keep it short

Biden's strategy needs to be threefold. Point number one is that less is more. He gets himself into trouble the longer he goes on. Particularly when he's playing defense, he should have a pithy one-liner ready to go and then move on to the next topic.

When Trump says Hunter Biden, Biden should say Ivanka traded on her dad to get trademarks for her business.

When Trump wears the mantle of law and order, Biden should say except when he is pardoning his crony buddies and encouraging violence.

When Trump says he's done more for Black people than any other president, Biden should point to the fact that his properties discriminated against Black tenants.

When he says "promises made promises kept," Biden should say his promises put kids in cages and destroyed our international standing.

We all know Trump's favorite soundbites by now. Biden must have a response ready to quickly turn them around.

It's the substance, stupid

The Republican focus on Biden's alleged cognitive failings was a losing strategy to begin with and also not true. If Americans voted on personal failings, neither Donald Trump nor Bill Clinton would have been elected. 

Joe Biden's second strategy is to stick to the key issues. Americans consistently prioritize substance over personality — and that works to Biden's advantage. He can play to his winning hand on the coronavirus response, on protecting healthcare, and on common sense gun safety — all issues where he holds the popular position. 

As he did throughout the Democratic primary race, Biden should also fall back on his strong political resume. For Americans unhappy with the Trump experiment, the idea of Joe Biden as the steady, experienced hand to take the tiller is a powerful message. Biden should pair talking about his current platform with examples of how he has gotten it done throughout his storied career.

The one issue where, according to polling, Trump trumps Biden is the economy. So Biden needs to talk about how Trump squandered our economic growth with his virus response and about how not every American is benefiting from our economy's growth. Biden presents as a regular guy, not an inheritor-in-chief, and if Americans trust that he can relate to their economic pain, they will reward him.

Closing argument

Americans have made up their mind about Trump. The question is whether they are comfortable with Biden as the alternative.

Republicans have served up the chance to make that case on a silver platter. After months of attacks on his cognitive fitness, Joe Biden can shatter expectations and prove that he is in fact better equipped to guide our troubled nation than the "stable genius" incumbent.

To do so, Biden's third strategy is to reassure the American people of a return to normalcy. As the outrage over the replacement for recently deceased Supreme Court Justice Ruth Bader Ginsburg began to boil over, Biden wisely shifted to cooling the rhetoric on all sides and healing across the board. As Trump goes goofy and outrageous, Biden must rise above it all. 

After four years of chaos, Americans crave a president who will simply Make America Normal Again. That is Joe Biden's brand. He is the antidote to Trump.

He also exudes charisma in a way that Trump never can. As the DNC so artfully captured, the consistent themes of Joe Biden's often tragic life story have been genuine compassion and a commitment to public service. Biden can speak to hearts on the debate stage and demonstrate to America the stark contrast in character with our current president.

With the polls being largely consistent over the course of the year, it seems that there's little that can move the race at this point. The debates are the last best opportunity for both candidates to make their case. If Biden is himself, with his heart on his sleeve and true experience under his belt, he will be our President in a few short months.