Joe Biden's campaign team accused Trump of showing "weakness" by claiming that him becoming president would "hurt God".
Speaking at an airport in Cleveland, Ohio, Trump described his conception of the United States under Biden.
No religion, no anything. Hurt the Bible, hurt God. He's against God, he's against guns, he's against energy. Our kind of energy.
I don't think he's going to do too well in Ohio.
Biden, a lifelong practising Catholic, has spoken publicly about his faith helping him through the death of his wife and children.
Trump's comments appear to have been prompted by his neck-and-neck polling numbers with Biden in Ohio, a crucial state he won by just eight points in 2016.
A spokesperson for Biden's campaign, Andrew Bates, accused Trump of desperation for attacking Biden's faith.
Joe Biden’s faith is at the core of who he is; he’s lived it with dignity his entire life, and it’s been a source of strength and comfort in times of extreme hardship.
Donald Trump is the only president in our history to have tear-gassed peaceful Americans and thrown a priest out of his church just so he could profane it – and a Bible – for his own cynical optics as he sought to tear our nation apart at a moment of crisis and pain.
And this comes just one day after Trump’s campaign abused a photo of Joe Biden praying in church to demean him, in one of the starkest expressions of weakness throughout this whole campaign.
Trump's latest campaign video includes out of context images of Biden, doctored to make him look dejected. People pointed out the differences between the original and edited photos by sharing them side by side. In one, Biden appears to be bowing his head in despair: he was actually praying in a church in Delaware.
In another, Biden's microphone was removed to make him appear "diminished".
And in another, he's accused of being "alone" despite being in a room full of people.
Biden also personally responded to Trump's comment that he would "hurt God".
Like so many people, my faith has been the bedrock foundation of my life: it's provided me comfort in moments of loss and tragedy, it's kept me grounded and humbled in times of triumph and joy.
And in this moment of darkness for our country — of pain, of division, and of sickness for so many Americans — my faith has been a guiding light for me and a constant reminder of the fundamental dignity and humanity that God has bestowed upon all of us.
For president Trump to attack my faith is shameful. It's beneath the office he holds and it's beneath the dignity the American people so rightly expect and deserve from their leaders.
Trump identifies as Presbyterian, but he is not generally known for his religious faith.
Pew research suggests that fewer than half of Americans think that Trump is a Christian, despite his efforts to engage this voter base by surrounding himself with evangelical leaders and lawmakers like vice president Mike Pence.
His attack on Biden's religion is unlikely to be effective, according to former Republic National Committee communications director Douglas Heye. He said:
We've seen these attacks before and they've just not been effective outside of a very small part of the Republican base.
You've made such over-the-top political attack that questions someone's faith, it's bound to not be effective.