To my knowledge, Trump made zero effort to extoll the virtues of communism or to denigrate the United States in any sort of public manner, which would be the only use for a semi-famous rich real estate dude in NYC. Much the opposite, he embraced capitalism.

...he didn't have to "extol the virtues of communism" to be useful to the U.S.S.R., and he didn't "sudden(ly), in his early '70s," decide to run for president. On the contrary, as the article mentions, he first floated a run for president in 1988 (only months after his visit to the Soviet Union), and again in 2000. In 1988, right at the end of the "Morning in America" era, his brief run included an open letter/advertisement in major papers calling for U.S. foreign policy to distance itself from N.A.T.O. and stop spending its defense funding on Japan. It doesn't take a master diplomat to realize that both of those proposals would have been music to the ears of the Soviet Politburo just as much as they would be to their current Russian successor.

When they groomed Trump in the '70s and '80s, did the KGB expect that Trump would eventually become president? Highly unlikely. But was it to their advantage to reel him in, with the expectation that he could become prominent in the Republican Party (and, being the very image of capitalist success would have made sure he was welcome there, or in the emerging "Third Way" Democratic wing, for that matter) and thus become a major voice for isolationism? I'm guessing that was their real goal, and it paid off admirably.