Donald Trump. Win McNamee/Getty Images

President Donald Trump kicked off the week with a series of tweets, one of which blasted Democrats as "OBSTRUCTIONISTS" and accused them of stalling confirmation of his executive-branch nominees.

But Trump hasn't nominated anyone for a majority of critical executive-branch positions.

Tweeting at Fox News' morning show "Fox and Friends" on Monday, Trump said: "Dems are taking forever to approve my people, including Ambassadors. They are nothing but OBSTRUCTIONISTS! Want approvals."

There are 559 key executive-branch positions that require Senate confirmation, according to a data tracker put together by The Washington Post and the Partnership for Public Service. Trump has not nominated anyone for 442, or 79%, of those positions.

The State Department, the agency under which ambassadors work, has 120 positions requiring confirmation. Eight of Trump's nominees have been confirmed and six are awaiting Senate confirmation, while 103 positions are open and have no nominee.

Of the 54 ambassador positions open, five have been nominated and four have been confirmed; 45 have no nominee.

Having a high number of unfilled positions across federal agencies is not a catastrophic risk in the short term, experts told Business Insider, because while political appointees await Senate confirmation, the administration has the power to appoint acting individuals to executive agency roles.

In other words, while the positions are unfilled, they are not vacant and are almost always occupied by career people who are chosen by the president from a narrowly defined pool, while the president's nominee is vetted by the Senate.

But experts warn the greatest risk in unfilled roles lies in handling crisis situations or enacting long-term policies.