Former US president Barack Obama took a veiled swipe on Tuesday at his successor Donald Trump, chastising those who "denied warnings" of a deadly coronavirus pandemic.
Mr Obama also warned against against ignoring the consequences of climate change after the administration finalised an overturn of his vehicle fuel economy and greenhouse gas emission standards aimed at slowing global warming.
"We've seen all too terribly the consequences of those who denied warnings of a pandemic," Mr Obama posted on Twitter.
"We can't afford any more consequences of climate denial. All of us, especially young people, have to demand better of our government at every level and vote this fall."
Mr Trump's administration has faced criticism for failing to heed early global alarms about the virus outbreak, after death tolls began to sharply rise in countries such as China and Italy.
The US has more than 166,000 confirmed coronavirus cases, the most worldwide, and the US death toll has surged past 3,400, exceeding China's official toll.
Mr Obama's tweet included a link to a story about the Trump administration's new rules.
Transport Secretary Elaine Chao said the Environmental Protection Agency and the Department of Transport were overturning "costly, increasingly unachievable fuel economy and vehicle carbon dioxide emissions standards".
The stringency of those standards will now be increased by 1.5 per cent a year until 2026, substantially less than the about 5 per cent annual increases issued in 2012, the EPA said.
So far, Mr Obama has rarely engaged in the 2020 presidential race, which features his former vice president Joe Biden as the Democrat most likely to face Mr Trump in November's election.
Mr Obama has not publicly endorsed any candidate in the Democratic nomination race, which has been reduced to Mr Biden and leftist Bernie Sanders.
