President Donald Trump and his party's effort to shift the federal courts to the right may be running out of road, with Democrats set to take control of the Senate next year.

During his first term, Trump placed more than 230 judges on the federal bench, including three Supreme Court justices. So far in his second term, the Senate has confirmed 57 of his judicial appointments. In total, Trump nominees now make up roughly one-third of the active federal bench. Because federal judges hold lifetime appointments, those confirmations will shape the direction of court rulings long after Trump leaves office.

But Democrats are now positioned to hold at least 54 Senate seats, and as many as 56, depending on outstanding results in Mississippi and Alaska, making it highly unlikely that Trump will fill many more vacancies on the U.S. district and appeals courts. Judicial confirmations require only a simple majority in the Senate — a threshold Democrats lowered for most nominees in 2013 and Republicans extended to Supreme Court picks in 2017 — meaning the incoming majority alone will control who reaches the bench.

"No one, or nearly no one, is going to get confirmed, so what he does in terms of nominating people, we'll see," Ed Whelan, a distinguished senior fellow at the Ethics and Public Policy Center and a former law clerk to the late Justice Antonin Scalia, told CBS News.

There are currently 28 vacancies on the federal courts, with another 15 set to open over the coming weeks and months. The president has formally sent 16 nominees to the Senate, and the GOP-controlled Senate Judiciary Committee is moving quickly to advance those appointments before the chamber changes hands. Any nominee not confirmed before the new Congress convenes in January would have to be renominated and would then face a committee controlled by Democrats.

Republicans are violating "numerous longstanding standards in a desperate attempt to confirm more than 30 qualified loyalists to lifetime appointments before Democrats take the majority," Sen. Dick Durbin (D-Ill.), the committee's senior Democrat, said on Tuesday.

Committee Chair Sen. Chuck Grassley (R-Iowa) dismissed Durbin's assertion that the panel was departing from its usual practice. "Historically, this committee has shortened timelines when circumstances warrant it," he said.

"The priority is going to be getting the judges across the finish line," Senate Majority Leader John Thune told reporters on Monday.

Even so, federal bench seats still open at the end of the current Congress are likely to remain unfilled for at least the next two years.

"What we've seen is the federal courts being stacked with extremists and loyalists, and now Democrats have the power to stop the reshaping of our courts in a very dangerous direction," said Rachel Rossi, president of the Alliance for Justice, a progressive judicial advocacy group.

Democrats' decisive rout of Republicans in last week's midterm elections also makes it highly unlikely that a Supreme Court justice appointed by a GOP president would retire during the final two years of Trump's term, since a successor would almost certainly fail to clear the Senate.

"Trump has managed to put in jeopardy his biggest achievement," Whelan said.