Your grandfather ditched the name Drumpf. Too German? And then there’s your new name, Trump:
For a long time afterward, all trumps were this noisy. A history of Richard I written 30 years later describes a regal scene: “They trumpyd, and her baners displaye of sylk.” When Myles Coverdale translated the Bible a century later, he described a similar scene during an ancient Judean battle: “The priests tromped with their trompettes.”
Even if they made a joyful noise, not all trumps were holy. “Trump also means, especially in British English, to, erm, break wind,” Maier told me. “That’s quite a common expression, and it’s related to trumpets as well.”
Trump has exuded this meaning for centuries. A Latin translation guide from the 1550s gave trump as a synonym for crepo, which it defined like this: “Trump or let a crackke, or fart.” (Crepo also means “to rumble,” “to resound,” and “to burst asunder,” in case you doubted what kind of trump this was.) All this trumping makes you wonder what locals think about Trump Turnberry, the current candidate’s hotel property in Scotland.
https://www.theatlantic.com/technology/archive/2016/10/ave-atque-trumpe/505259/
See also trumpery:
trumpery
noun
1
a
: worthless nonsense
b
: trivial or useless articles : JUNK
a wagon loaded with household trumpery
2
archaic : tawdry finery
trumpery adjective
Trumpery derives from the Middle English trompery and ultimately from the Middle French tromper, meaning "to deceive." (You can see the meaning of this root reflected in the French phrase trompe-l'oeil-literally, "deceives the eye"-which in English refers to a style of painting with photographically realistic detail.) Trumpery first appeared in English in the mid-15th century with the meanings "deceit or fraud" (a sense that is now obsolete) and "worthless nonsense." Less than 100 years later, it was being applied to material objects of little or no value. The verb phrase trump up means "to concoct with the intent to deceive," but there is most likely no etymological connection between this phrase and trumpery.
https://www.merriam-webster.com/dictionary/trumpery