Herschel Walker, the GOP candidate, lost the Georgia Senate runoff to his Democratic rival on Tuesday.
Walker's son said his father ran after Trump called for months, "demanding" that he do so.
His son said "everyone with a brain" urged Walker not to run due to his "insane past."
Herschel Walker's son said his father ran in Georgia's Senate race after former President Donald Trump spent months demanding he do so, even as others begged him not to enter the race over his "insane past."
Walker was defeated in the Senate runoff on Tuesday, by Democrat Raphael Warnock, after a campaign that was marked by allegations against him, including that he paid for women to have abortions despite having a strict, pro-life stance.
His son, Christian Walker, tweeted on Tuesday that his father had rejected calls not to run, after being repeatedly told to enter the race by Trump.
"The Truth: Trump called my dad for months DEMANDING that he run," Christian Walker said.
"Everyone with a brain begged him: 'PLEASE DON'T DO THIS. This is too dirty, you have an insane past… PLEASE DONT DO THIS.' We got the middle finger. He ran."
He also accused the Republican Party of only running his father in the election because of his skin color.
"Republicans, we say we don't play 'identity politics' and then you ran this man mainly because he was the same skin color as his opponent with no background other than football. A boring old Republican could have won," he wrote.
Christian Walker, who is estranged from his father, publically criticized Herschel Walker during the election campaign.
In October he accused Walker of lying and of abusive behavior, after it was first reported that he had urged and paid for a woman he was dating in 2009 to get an abortion.
"You're not a 'family man' when you left us to bang a bunch of women, threatened to kill us, and had us move over 6 times in 6 months running from your violence," he wrote on Twitter.
Despite this, he remained generally quiet through much of the campaign, but said on Tuesday that he could speak freely now that the election was over and he did not risk driving too many voters to the Democrat, according to The New York Times.
The Times referred to Christian Walker as a right-wing influencer who has supported Trump.
During the Senate campaign Herschel Walker was accused of hiding "secret" children and of pressuring two women to have abortions, which he has denied.
An ex-girlfriend also accused him of attacking her, after she caught him with another woman. Walker has not commented publicly on the allegation.
Walker's defeat means that the Democratic Party gained an outright majority in the Senate, with 51 seats compared to 49 for the Republican Party.