The deputy prime minister used a column in the Times to attack the foreign secretary who has pledged to reduce taxes in her bid to become party leader.
Mr Raab, a supporter of Mr Sunak, said Ms Truss’s plan would damage the living standards of millions to the point where the Conservatives would face “impotent oblivion” at the next election.
Meanwhile, Mr Sunak has outlined his own pledges to halt the cost of living crisis. He has suggested that under his leadership every household would get £400 off their energy bills, while those on means tested benefits would receive a further £650. The Truss campaign described his move as a “mammoth strategic U-turn,” questioning how it would be funded.
However, Mr Raab has backed Mr Sunak, and said that unlike Ms Truss, the former chancellor showed pragmatism.
He wrote: “All the evidence overwhelmingly tells us that, with inflation running high and energy bills the highest they’ve been for decades, the winter will be extremely difficult.
“Those pressures are well beyond the living memory of millions of voters, and will directly affect millions more.”
Mr Raab added: “If we go to the country with an emergency budget in September that fails to measure up to the task in hand, voters will not forgive us as they see their living standards eroded and the financial security they cherish disappear before their eyes.
“Such a failure will read unmistakenly to the public like an electoral suicide note and, as sure as night follows day, see our great party cast into the impotent oblivion of opposition.”