Think it was a revival of a classic anthology series. A scientist has an enemy who is about to seize power, shutting down time travel project. Using a prototype time machine, scientist travels back into the past, shoots and kills his enemy. Then, in the present, just as he is about to announce his takeover, enemy suddenly crumbles to dust as if he'd been dead for years!
"The Evil Touch" (1973 TV series)? (Episode 15: Campaign 20)
You said it was '70s and an anthology episode and this one seems to be a match, but as I can't find anything online about it I can only upload this plot description from IMDb.
"World-renown scientist David Zack is trailing his opponent in the 2020 presidential campaign. He schemes to use his latest invention, a time-travel machine, to make sure his competitor is never born. He sends a humanoid to the past to prevent the man's parents from ever meeting."
I think I've found the episode on YouTube and I'm editing it in. Here it is: