President Donald Trump has taken a shot at an ailing former president, George HW Bush.

Speaking at a rally in Montana on Thursday, Trump mocked a phrase that Bush made famous when he successfully ran for president in 1988.

‘You know all of the rhetoric you see. “Thousands points of light.” What the hell was that by the way?’ Trump said to a crowd of supporters in Great Falls.

Trump's remarks were reported by CNN.

‘Thousand points of light’ is a reference which Bush made during his speech before the Republican National Convention in 1988.

Bush, who was vice president at the time, was speaking about volunteer organizations and youth clubs as ‘a brilliant diversity spread like stars, like a thousand points of light in a broad and peaceful sky.’

He eventually used the phrase again during his inauguration speech.

President Donald Trump has taken a verbal shot at an ailing former president, George HW Bush. Speaking at a rally in Montana on Thursday, Trump mocked a phrase that Bush made famous when he successfully ran for president in 1988

Trump on Monday referenced 'thousand points of light,' a phrase which Bush coined during his speech before the Republican National Convention in 1988 in New Orleans (above)

In 1990, Bush created the Points of Light Foundation, which promoted non-governmental solutions to social problems.

In the 90s, Saturday Night Live comedian Dana Carvey imitated Bush and frequently used the phrase ‘thousand points of light.’

During Thursday’s Montana rally, Trump said: ‘Thousand points of light.’

‘What does that mean? I know one thing. Make America Great Again we understand.

‘Putting America first we understand.

‘Thousand points of light, I never quite got that one. What the hell is that?’

‘Has anyone ever figured that one out? It was put out by a Republican wasn't it.’

Ari Fleischer, who was White House Press Secretary to President George W. Bush, tweeted in response: 'This is so uncalled for. Going after a 94-year-old, former President’s promotion of volunteerism. I don’t mind potus being a fighter. I do mind him being rude.'

Reaction on Twitter was largely negative as Trump was blasted for his comments

'George H.W. Bush's reference to a Thousand Points of Light has endured for three decades, motivating action by every president since, and inspiring millions around the world,' tweeted author Michael Wear.

'Trump's presidency will produce nothing like it. It's the difference between a huckster and a statesman.'

The attack was particularly insensitive given that Bush recently became a widower following the death of his wife, former First Lady Barbara Bush.

Trump was absent from Barbara Bush’s funeral - reportedly because the Bush family insisted it did not want him there.

First Lady Melania Trump attended the funeral in her husband’s place.

Shortly after the funeral, George HW Bush was admitted into the hospital, but he recovered.

Bush, the 41st president, has been in and out of the hospital in recent years due to failing health and old age.

Trump has been harshly criticized for attacks on another ailing Republican.

Earlier during the rally, Trump once again made reference to Senator John McCain, criticizing him for voting against the Republican-led repeal of Obamacare.

George HW Bush was photographed earlier this week. His granddaughter, Lauren Bush Lauren, posted an image on social media showing her two-month-old son Max finally meeting his great-grandfather for the first time

McCain is currently receiving treatment for an aggressive form of brain cancer.

The Trump and Bush families have been warring since Trump’s attacks on the elder Bush; his son, former President George W. Bush; and his other son, former Florida Governor Jeb Bush, who lost to Trump during the GOP primary in 2016.

Last month, Jeb Bush criticized the Trump administration for its policy of separating children from their parents at the border.

In response, the president’s eldest son, Donald Trump Jr., canceled an appearance at a fundraiser for Jeb Bush’s eldest son, George P. Bush, in New York City.

George HW Bush was photographed earlier this week.

His granddaughter, Lauren Bush Lauren, posted an image on social media showing her two-month-old son Max finally meeting his great-grandfather for the first time.

The proud mother, 34, took to Instagram on Monday to share a photo of her grandfather, 94, happily holding Max, who is nearly 11 weeks old, in Kennebunkport, Maine.

She captioned the family snap: 'Max meeting his great-Gampy,' along with a blue heart emoji.