Depends on what you mean.

But generally I’d say no felonies, no drugs (convictions and/or test results) and no strong ties to foreign governments. But the details will vary a bit.

No drugs, specifically cannabis. I've heard that admitting to using cannabis in the past gets you tossed, despite it being common, safe, and legal in much of the country.

In the late 80s to early 90s as I attended college and then spent a couple of years following the Dead, I smoked pot, ate mushrooms, dosed LSD, and snorted cocaine on a regular basis. I also sampled various other substances along the way.

Several years later I applied for and received a Top Secret clearance. I fully admitted all prior drug use as part of the process. I was working for a government contractor at the time and was not a government employee.

At the same time I had a couple of friends who worked for a 3 letter agency and had prior regularly smoked pot. They admitted their prior use during the hiring process. This again was during the late 90s when attitudes towards pot were more negative than they are today.

Past drug use does not disqualify you. Source: have friends who smoked pot and got security clearances.

Lying about it (if caught) will absolutely get you disqualified though.

But yeah use and conviction are very different.