President-elect Donald Trump can quickly put his imprint on the Federal Reserve given two existing vacancies on the seven-member board of governors, but he is likely to have to wait until 2018 to change the leadership of the central bank, analysts said Wednesday.

There are two vacancies on the Fed because Senate Republicans this year blocked a vote on President Barack Obama’s two nominees to the central bank: Allan Landon, a former Bank of Hawaii executive, and Kathryn Dominguez, a professor at the University of Michigan, over a dispute over who at the Fed would oversee the central bank’s new powers to oversee Wall Street.

Ian Shepherdson, chief economist at Pantheon Macroeconomics, said Trump was likely to nominate two “hard money” candidates.

“A core view of many Trump advisors is that the extended period of emergency policy settings has promoted a bubble in the stock market, depressing the incomes of savers, scared the public and encouraged capital misallocation,” Shepherdson said.

“Right now, these are minority views on the Fed policy-making committee, but Trump appointees are likely to shift the needle,” he said.

Fed Chairwoman Janet Yellen’s term expires in February 2018. Fed insiders say the don’t think she will leave early even though Trump has criticized her for being political.

Read: Donald Trump accuses Yellen, Fed of politicizing interest rates

Other presidential candidates have criticized the Fed leadership and none have ever resigned, noted Robert Perli, a partner at Cornerstone Macro LLC in Washington and former associate director of monetary affairs at the central bank.

“I would be surprised [if Yellen left], I don’t see what good could come from that to her or the institution,” he said.

Former Minneapolis Fed President Narayana Kocherlakota, now a professor at the University of Rochester, said there was likely to be near-term economic uncertainty associated with the Trump administration.

“Yellen’s staying is, I think, highly desirable in order to provide the monetary policy continuity needed to help mitigate that uncertainty,”Kocherlakota said in a research note.

Andrew Levin, a former top adviser to former Fed Chairman Ben Bernanke and now an economics professor at Dartmouth College, said he couldn’t predict what Yellen would do but added it would be important for the Fed for her to finish her term.

“It’s important for the Fed and the strength of the institution that it be insulated from short-term political movements and certainly having the Fed chairwoman serve out her full four-year term, even if it extends into a new administration, is an important way the Fed works,” Levin said.

Yellen’s No.2 Stanley Fischer’s four-year term is also set to expire in 2018. Levin said it would be unusual for a vice chairman to only serve more than one term.

Another challenge for the Fed is that the Republican Congress is likely to consider legislation to reform the central bank.

“It’s been a priority for Republicans and I am assuming it is going to come up in the coming year,” he said.

The House last year passed legislation that would require the Fed to set a policy rule. The 2016 Republican platform called for an annual audit of the central bank’s interest rate decisions, something the central bank has said would put unwanted political pressure on monetary policy.