The ink was barely dry on President Trump’s acquittal when Republican Sens. Charles E. Grassley (Iowa) and Ron Johnson (Wis.) announced they would be investigating Hunter Biden — just as Trump had wanted Ukraine to do.

In a letter sent Wednesday to the head of the Secret Service, the senators write that they are “reviewing potential conflicts of interest posed by the business activities of Hunter Biden and his associates during the Obama administration, particularly with respect to his business activities in Ukraine and China.”

Specifically, they are seeking from the Secret Service any instances when Hunter Biden traveled with protective security detail during the time his father, Joe Biden, was vice president, as well as when he flew on government planes.

Trump’s impeachment centered on his desire for an investigation into Hunter Biden and, by extension, Joe Biden, his potential 2020 opponent. The president was charged by the House in December with abuse of power for allegedly withholding military aid to pressure Ukraine to publicly announce an investigation into the Bidens. The Senate voted Wednesday to acquit him.

The letter mentions Hunter Biden’s position on the board of the Ukrainian energy company, Burisma, while his father was the Obama administration’s point person on Ukraine policy. Trump and Republicans have claimed, without evidence, that there was something nefarious in the Bidens’ dealings with Ukraine.

Trump and his allies have focused primarily on Biden’s push to have Ukraine’s top prosecutor, Viktor Shokin, removed — a position supported at the time by other Western leaders who said Shokin was not doing enough to root out corruption in Ukraine. The prosecutor had previously investigated Burisma, but the probe was dormant at the time, according to former Ukrainian and U.S. officials.

Throughout the House impeachment hearings, Republicans sought to shift the narrative to focus on the Bidens. They asked for Hunter Biden to testify, which the Democrats rejected as irrelevant to the question of whether Trump abused his power.

Senate Republicans used Democrats’ refusal to call Hunter Biden as a witness as a reason they would not allow additional witnesses in the Senate trial.

Kurt Volker, former U.S. special envoy to Ukraine, said during his House testimony that “allegations against Vice President Biden are self-serving and not credible.”

If Biden becomes the Democratic presidential nominee, it’s possible Republicans and the White House could elevate the inquiries, as they did with Hillary Clinton over her use of a private email server.

Grassley and Johnson are not the first Senate Republicans to launch an investigation into the Bidens.

During House impeachment proceedings in November, Sen. Lindsey O. Graham (R-S.C.) sent a letter to Secretary of State Mike Pompeo requesting documents on the former vice president and his communications with Ukraine.

Graham’s inquiry is focused on any calls Biden had with the Ukrainian president at the time, Petro Poroshenko, regarding the firing of the country’s top prosecutor and any reference to an investigation into Burisma.

Graham said Sunday on Fox News that he and other Republicans would begin calling witnesses for hearings related to Hunter Biden, and that he “can prove beyond any doubt that Joe Biden’s effort in the Ukraine to root out corruption was undercut because he let his son sit on the board of the most corrupt company in the Ukraine, and we’re not going to give him a pass on that.”