Trump turns 78, a birthday he says he'd like to pretend 'doesn't exist,' during age-focused election

Not all birthdays are worth celebrating in the eyes of former President Donald Trump, who marks his 78th birthday on Friday.

"There's a certain point at which you don't want to hear 'Happy Birthday.' You just want to pretend the day doesn't exist," Trump quipped to his supporters last week at a rally in Las Vegas after they broke out in song for him ahead of his birthday.

Still, the former president is not missing out on the chance to campaign on his birthday -- marking his 78th with a sold-out speech in West Palm Beach Friday evening in front of his most fervent supporters: members of his "Club 47" fan group.

On Thursday, Trump also received an early birthday celebration from congressional Republicans, who sang for him during their closed-door meeting on Capitol Hill, sources told ABC News. They presented him with a cake with the numbers "45" and "47" as they rallied behind him in a show of force ahead of November's election.

However, in an election year where age remains a focal points for both candidates, Trump has attempted to highlight mental fitness and competency instead of age as he edges closer to the age of his opponent, President Joe Biden.

"Joe Biden is not too old to be president. I know a lot of people that are older than me. They're at the top of their game. It's not even close. But he is too incompetent," Trump said in a video posted on his social media platform last week.

Trump repeated his claim that Biden is incompetent -- not old -- during his most recent rally in Las Vegas, even questioning the sitting president's intelligence.

"This guy -- there's just something missing," Trump said. "There always has been -- by the way, he always had the worst and dumbest foreign policy."

Trump was able to fend off his younger Republican challengers during the primary as they launched attacks on his age, calling for a new generation of leadership.

"I feel my mind is stronger now than it was 25 years ago. Is that possible? I really do," Trump said at a rally in January, responding to criticisms from former United Nations Ambassador Nikki Haley about his age. "Now Biden can't say that, you know he can't say that."

Trump said something similar at a New Hampshire rally in January.

"I feel like I'm about 35 years old. I actually feel better now than they did 30 years ago. Tell me, is that crazy?" Trump said. "I feel better now. And I think cognitively I'm better than I was 20 years ago. I don't know why."

He has also routinely bragged about "acing" the Montreal Cognitive Assessment test, a test doctors use to uncover early signs of cognitive impairment, while in the White House.

"Only about 2% in this room can do it, but I did it. I did it very easily," Trump said about his results on the test at an event in Las Vegas in January. "But I got mocked -- they said, 'Oh, that's so easy.' It's not easy. It's not easy. Go home and try doing it."

The Trump campaign has started fundraising off the former president's birthday, blasting out numerous fundraising emails to followers, asking them to sign his virtual birthday card and a donation in celebration of his birthday.

"Birthdays are incredibly important in our family, and we're counting on your help to make President Trump's birthday celebration his BIGGEST one yet! Our goal is to collect 1 MILLION signatures from Patriots like YOU wishing him a 'happy birthday,' but we're missing yours," the email reads.

The Biden campaign is using Trump's birthday to highlight his stumbles throughout his professional and political life, releasing a list of "78 of Trump's historic ... 'accomplishments,'" which include his felony convictions as well as digs at his business ventures into steak, vodka and water.

"Happy birthday, Donald. You're a crook, a failure, a fraud, and a threat to our democracy, economy, rights, and future," Biden campaign spokesperson James Singer said in a statement. "On behalf of America, our early gift for your 79th: Making sure you are never President again."

Biden has repeatedly been forced to defend his mental fitness and age due to persistent gaffes; however, his campaign has leaned into his old age, highlighting how it shows he has extensive experience to address the nation's problems.

In a campaign ad released earlier this cycle, Biden acknowledged his advanced age directly.

"Look, I'm not a young guy," Biden said with a chuckle at the start of the ad, speaking directly to camera. "That's no secret. Here's the deal, I understand how to get things done for the American people."

On Biden's 81st birthday in November, the Trump campaign released a limited, generic physical exam from Trump's doctor.

"It is my opinion that President Trump is currently in excellent health, and with his continued interest in preventative health monitoring and maintenance, he will continue to enjoy a healthy active lifestyle for years to come," Dr. Bruce Aronwald wrote in the letter.

Trump's physician added Trump's physical exams were "well within the normal range" and his cognitive exams "were exceptional."

However, while Trump and his campaign look to highlight Biden's gaffes and blunders, the presumptive Republican nominee has had his own share of slip ups.

Throughout the campaign trail, Trump has mixed up former House Speaker Nancy Pelosi with Haley -- and former President Barack Obama with Biden. Both times, the campaign has attempted to clean up his comments by stating "its a distinction with a difference."

And as Trump often boasts about his strong mind and ability to talk off the cuff, at his most recent rally in Las Vegas, where he claimed the teleprompters weren't working because of the high heat temperatures, the former president delivered a freewheeling, tangent-filled speech.

Yet still, despite the fact that polls show that voters agree that both Biden and Trump are too old to hold office for another term, they show more concern for Biden's mental fitness compared to Trump.

In a Marquette University poll from last month, 79% of respondents said the phrase "too old" describes Biden "very or somewhat well," compared to 54% saying the same of Trump.

In another poll from ABC News/IPSOS in May, people were asked which personal attributes apply to either candidate more. Trump led Biden on mental sharpness 42%-23% with 34% saying it applies to neither. On physical health, Trump again led Biden 42%-20%, with 37% applying the word to neither.