When Russia interfered in the 2016 U.S. presidential election, spreading divisive and inflammatory posts online to stoke outrage, its posts were brash and riddled with spelling errors and strange syntax. They were designed to get attention by any means necessary.

       “Hillary is a Satan,” one Russian-made Facebook post read.

       Now, eight years later, foreign interference in American elections has become far more sophisticated, and far more difficult to track.

       Disinformation from abroad — particularly from Russia, China and Iran — has matured into a consistent and pernicious threat, as the countries test, iterate and deploy increasingly nuanced tactics, according to U.S. intelligence and defense officials, tech companies and academic researchers. The ability to sway even a small pocket of Americans could have outsize consequences for the presidential election, which polls generally consider a neck-and-neck race.

       Russia, according to American intelligence assessments, aims to bolster the candidacy of former President Donald J. Trump, while Iran favors his opponent, Vice President Kamala Harris. China appears to have no preferred outcome.

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       But the broad goal of these efforts has not changed: to sow discord and chaos in hopes of discrediting American democracy in the eyes of the world. The campaigns, though, have evolved, adapting to a changing media landscape and the proliferation of new tools that make it easy to fool credulous audiences.

       Here are the ways that foreign disinformation has evolved:

       Now, disinformation is basically everywhere. Russia was the primary architect of American election-related disinformation in 2016, and its posts ran largely on Facebook.

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