It's not a bad thing, but I'm not sure how much Trump can be credited with it.
But as for the "unemployment rate," I've always considered to be a deceptive figure because it's not calculated in any meaningful way.
Doing a bit of checking on a few sites and number crunching, I have calculated that the US population of those aged 18-64 was approximately 207 million in 2016 (based on US Census data). According to the BLS, there were approximately 124 million full-time employees in the US during the same year.
Out of 207 million, that would leave 83 million people unemployed, which would be an unemployment rate of about 40%.
To try to calculate it any other way is blatantly dishonest.
You might try to read up on how these figures are determined, and different kinds of "employment" and "unemployment" are determined, and yes, there are several different kinds.
To begin with, you don't count active-duty military, so that has to be accounted for. Then, there are some people over the age of 64 who do work, even when they are "retired," so adjustments need to be made for that tidbit. Those in prison or jail are not included. The numbers include those over age 16, not starting at 18. Those who are disabled and unable to work are accounted for. The self-employed are not included. And, there are a significant number of adults who, for various reasons, do not wish to work, and are not actively seeking employment, including the retired and spouses/partners. Part-time workers, and those who work two or more jobs must be accounted for.
Then, the current rates are determined based on a model of the economy, and includes data from a number of different sources, including monthly surveys of households, news reports, employer reports to government, etc., etc.
It's complicated because life is complicated, and while the DOL does report a simple number such as you suggest, that statistic is almost worthless to various consumers of employment data, including the states, localities, nonprofits, etc., who have to administer various programs that might have to deal with the unemployed in some way or another.