Donald Trump Carlos Barria | Reuters

More than five months into his presidency, President Donald Trump is starting to fill out the executive branch more quickly. But he still lags behind his predecessors in filling jobs — and many departments in his administration remain thin. As of Wednesday, Trump had formally nominated 178 people to positions that require Senate confirmation, with 46 appointees confirmed, according to the Partnership for Public Service, a nonprofit organization that tracks the pace of presidential nominations. He trails the pace set by Presidents Barack Obama, George W. Bush, Bill Clinton and George H.W. Bush — but he has started to catch up relative to his predecessors since the end of May. The numbers exclude judicial nominations — many of which Trump has made — and noncivilian positions. Here are how Trump's nominations compare with the four presidents who served before him, though the numbers are not perfectly comparable because the presidents filled different numbers of positions:

Trump had formally nominated only 110 people to positions tracked by the Partnership for Public Service as of May 31. He has nominated 68 since, an increase in his pace. But the executive branch remains broadly understaffed, which can affect policy across the government, said Max Stier, president and CEO of the Partnership for Public Service. "When you talk about 46 people confirmed, it's pretty much everywhere that you've got substantial glaring holes. ... This is not a localized problem. It's everywhere," Stier said. Trump "is primarily slowing himself down — by imposing loyalty tests, requiring multiple staffers to sign off, and acting erratically," according to Anne O'Connell, a law professor at the University of California, Berkeley, who has studied the presidential appointment process. Still, some factors going for Trump could speed up his nominations, she said. In particular, a 2013 rules change means nominees can get through with only a majority vote in the GOP-controlled Senate — something that already saved some Trump picks like Education Secretary Betsy DeVos.

Potential trouble spots