President Trump has yet to nominate anyone for 74% of key executive branch positions. Out of the 558 positions which require Senate confirmation, 415 have no nominee as of Sunday.

Seven people have been announced as nominees but not formally nominated.

But the Trump administration's lag in selecting nominees may not be the only thing to blame for the White House's hiring crisis. Of the 94 formal nominees, the Senate has confirmed only 42 so far.

A number of factors besides the lack of nominees have also contributed to the delay, including: Democrats' opposition to Trump's nominees, some Republicans' unwillingness to work for an administration rocked by controversy, and Trump's reported treatment of administration officials.

Here's a guide to the reasons:

Trump's nominees have had to wait far longer than Obama's, Bush's, and Clinton's.

According to The Washington Post, Trump's Cabinet nominees had to wait 25 days between being officially nominated and being voted on by the Senate. On the other hand, President Barack Obama's nominees had a median wait time of two days, President George W. Bush's waited zero days, and President Bill Clinton's waited one day.

A number of Trump's nominees faced a steep uphill climb during their confirmation hearings. Secretary of State Rex Tillerson and Attorney General Jeff Sessions faced particularly sharp questioning from congressional Democrats for their past conduct, and Secretary of Education Betsy DeVos' nomination nearly failed after two Republican senators voted against her, leading to a 50-50 stalemate. In the end, Vice President Mike Pence had to cast the tie-breaking vote to confirm DeVos.

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Some Republicans are wary of joining the Trump administration amid the brewing Russia controversy.

reach some top White House officialsPolitico reported

The Trump-Russia story has gained even more steam since then, following Trump's abrupt decision to fire FBI director James Comey, a slew of media reports that raised questions about the president's and his associates' ties to Russia, and Comey's bombshell testimony before the Senate earlier this month.

A number of potential nominees are having second thoughts as the continuing investigations threaten to derail Trump's agenda, four people close to prospective nominees told Politico. Others echoed similar sentiments to The Washington Post in a story published Saturday.

An attorney who represents potential executive branch nominees also told Politico that three clients said they were not interested in working for Trump after former FBI director Robert Mueller was appointed as a special prosecutor to spearhead the FBI's Russia probe.

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Trump's treatment of current administration officials may be deterring potential appointees.

The Post reported that some potential nominees are aware of Trump's reported mood swings and frequent irritation toward senior staff and Cabinet members.

"Trump is becoming radioactive, and it's accelerating," Bill Valdez, a former senior Energy Department official, told the Post. "He just threw Jeff Sessions under the bus."

Valdez was likely referring to reports that Trump is angry with Sessions for recusing himself from the Russia probe. Sessions reportedly offered to resign over the tiff.

Trump has also frequently made statements that directly contradicted those his communications staff and spokespeople have made. This was perhaps most prominent in the immediate aftermath of Comey's firing.

The White House and Trump's spokespeople initially said that Trump's decision to remove the FBI director was based entirely on the recommendation of Deputy Attorney General Rod Rosenstein and had nothing to do with the escalating Russia controversy.

Shortly after, however, Trump told NBC's Lester Holt that he had already made the decision to fire Comey and was going to do it regardless of Rosenstein's recommendation. He also added that "this Russia thing" was a factor in his decision.

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