A Washington Post article that describes President Trump's pardons over the last few days says the following:
The move sparked blowback, mostly from Democrats, who accused him of wielding his executive authority to shield himself from possible criminal investigation.
How would Trump's pardoning of other people protect himself from any potential criminal investigation in the future? People who have been pardoned could still be subpoenaed in a future investigation. Wouldn't the only way for Trump to protect himself be to pardon himself, which he has not done yet?