True to his campaign promise, President Trump ordered a federal hiring freeze on Monday. His Contract with the American Voter said a freeze would be part of his “100-day action plan to Make America Great Again,” but Trump issued it on the first Monday of his presidency.

What does this mean for federal employees? Here are a few questions and answers:

Are all federal employees affected?

No. The wording of his memorandum exempts “military personnel” and says “the head of any executive department or agency may exempt from the hiring freeze any positions that it deems necessary to meet national security or public safety responsibilities.”

“Military personnel” generally refers to those in uniform, but if Trump also means civilian employees of the Defense Department, that alone would exclude about a third of the workforce.

Exempting public safety could wall off much of other large agencies such as the Justice Department and the Department of Homeland Security. If public safety includes public health workers, more would be excluded.

Why did he freeze federal hiring?

White House press secretary Sean Spicer cited money “wasted in Washington on a job that is duplicative. . . . We’ve got to look at how we’re spending the American people’s tax money.”

During the campaign Trump said a freeze would clean up corruption and collusion. How would that apply to job candidates who don’t yet have federal jobs?

Trump’s contract didn’t say, nor did he address that in his memorandum.

How would a freeze be implemented?

Trump’s order says “no vacant positions existing at noon on January 22, 2017, may be filled and no new positions may be created, except in limited circumstances.” The directors of the Office of Management and Budget and the Office of Personnel Management were told to “recommend a long-term plan to reduce the size of the Federal Government’s workforce through attrition. This order shall expire upon implementation of the OMB plan.” The memorandum also “does not revoke any appointment to Federal service made prior to January 22, 2017.”

What have we learned from previous hiring freezes?

In 1982, the Government Accountability Office said freezes under Presidents Ronald Reagan and Jimmy Carter were “ineffective in managing federal employment.” That report said the previous freezes “disrupted agency operations, and in some cases, increased costs to the Government.”

Will a freeze on federal employment mean agencies will hire more government contractors?

Federal labor leaders fear that could be the case. American Federation of Government Employees President J. David Cox Sr. said, “President Trump’s federal hiring freeze will result in more government waste as agencies are forced to hire high-priced contractors to do the work that federal employees can and should be doing.”

Has federal employment grown over the years?

Spicer cited a “dramatic expansion of the federal workforce in recent years.” While the absolute number of federal employees has increased, there are fewer federal staffers now compared with the size of the population they serve. “Since the 1960s, the U.S. population increased by 67 percent, the private sector workforce increased by 136 percent,” according to President Obama’s fiscal 2017 budget document, “while the size of the Federal workforce rose about 10 percent.”

Trump said the freeze will use attrition to cut jobs. How much turnover is there in federal jobs?

Government data shows that turnover has averaged about 210,000 jobs a year over the past five years, out of a workforce of just under 2.1 million. There are various ways of counting federal employment, and thus, turnover. Those figures include executive branch employees outside the U.S. Postal Service and intelligence agencies, but they include part-time, seasonal and temporary employees.

Of those who leave each year, about 75,000 on average quit, 65,000 retire and 55,000 leave because their appointments expire, which is common among temporary employees. About 10,000 are fired. The other separations are due to various reasons, including layoffs and deaths.