MathAmateur said:
Hard. Even after one of the characters above hire you, only 50% of the new tenure track profs eventually get tenure. I work with a lot of would be profs who never made tenure and all of these "losers" are really really smart.
While there is a lot of variation, that number seems high. A few set-up comments:
1) Since the institution loses the start-up funds if a hire does not obtain tenure, there is some built-in pressure/desire to hire people likely to obtain tenure.
2) Tenure is granted based on *many* levels of approval: department committee, department chair, college committee, dean, provost, president, and finally, the board of trustees all have to agree to award tenure. Because people make these decisions and everyone is an individual, everyone involved emphasizes different criteria: student evaluations, extramural research dollars, peer-reviewed published material, external evaluations, outreach, etc. etc.
3) "Tenure" itself means different things at different places. In general, it does not guarantee a salary, office or lab. It does not guarantee a job for life- the President or Board can fire tenured faculty. Tenured faculty are simply guaranteed a hearing prior to being fired.
At my previous institution, a Carnegie R1-designated school, the 'failure rate' was AFAIK, about 10% and probably lower. There, a person was required to have either multiple NIH R01 or a R01 *renewal* in order to be considered. R01's last 5 years and the tenure clock is 6 years, so if you didn't have a single R01 by year 2, you got a terminal appointment pretty quickly, and I know 3 people who got bounced (out of 30+ hires). They went to other research institutions and are currently doing quite well.
I'm currently at an R2 institution, and the failure rate is vanishingly small- and I say this hoping not to jinx myself- to the point where people remember the one or two folks (out of the hundreds of hires) who, didn't do what their review committees asked them to do- reasonable things.