Donald J. Trump hosted “Saturday Night Live” this past weekend and gave interviews to at least four national television networks on Sunday. The result: an opportunity to reach millions of potential voters, without spending a dime.

In fact, while many of his Republican presidential rivals have poured money into the airwaves in search of such exposure, Mr. Trump has not spent any money at all on television advertising since he announced his candidacy in June. Yet he has remained at or near the top of most national and state polls for months.

“TV ads are necessary, they can be effective, but in terms of overall value, being the host of ‘Saturday Night Live’ is probably going to get you a lot more as a candidate than 20 ‘super PAC’ ads,” said Dave Levinthal, senior political reporter at the Center for Public Integrity.

Thirty-second television commercials were once signs of a confident, well-financed candidacy for the White House. Now they are seen as a last resort of struggling campaigns that have not mastered the art of attracting the free media coverage that has lifted the political fortunes of insurgent campaigns like those of Mr. Trump and Ben Carson, a retired neurosurgeon who has surged to the top of the polls.