Collins was charged with insider trading, accused by federal prosecutors of tipping off his son about a biotechnology company's failed drug trial to avoid significant investment losses. The alleged tip-off took place not during the Obama Administration, as Trump's tweet suggests, but in 2017, after Trump had become president.
Hunter was charged with using more than US$250,000 in campaign funds for personal expenses, including family holidays, school tuition and theater tickets.
Collins has suspended his re-election campaign, while Hunter is running for re-election, alleging political bias by the Justice Department.
A few minutes after the tweet on Sessions, Trump added a second tweet attacking former FBI Director James Comey, asserting that Democrats did not like Comey until Trump fired him in 2017.
"The Democrats, none of whom voted for Jeff Sessions, must love him now. Same thing with Lyin' James Comey. The Dems all hated him, wanted him out, thought he was disgusting - UNTIL I FIRED HIM! Immediately he became a wonderful man, a saint like figure in fact. Really sick!"
The tweet on Sessions was an unusually harsh salvo, even for a president who sometimes expresses his inner thoughts on Twitter to the chagrin of his staff. The tweet indicated that his Attorney-General should base law enforcement actions on how it could affect the President and the Republican Party's electoral success. It also seemed to indicate electoral popularity should influence charges.
There has typically been a separation between the White House and the Justice Department, but Trump has frequently disregarded those norms, giving orders to Sessions. Sessions recently pushed back, saying publicly that he will not allow political manipulation of the department.
Trump recently told Bloomberg News that he would keep Sessions as Attorney-General until after the Midterm elections.
Trump's attacks on Sessions - and his efforts to force his Attorney-General to quit his post after Sessions recused himself from the investigation into Russia's interference in the 2016 election - are now part of an obstruction investigation into the President by Special Counsel Robert Mueller and his team.
Trump's conduct in firing Comey is also under investigation, particularly why he fired Comey and whether he pressured Comey to be generous to Michael Flynn, Trump's former national security adviser. Flynn has pleaded guilty to lying to the FBI.