Vivek Ramaswamy, a wealthy newcomer in politics who aligned himself with Trump, has decided to step back from his campaign.

A self-funded entrepreneur, Mr. Ramaswamy reached the height of his popularity in late August but faced a decline under attacks from his opponents. Following his withdrawal post the Iowa caucuses, he expressed support for Donald J. Trump.

Vivek Ramaswamy, a 38-year-old entrepreneur and political novice who briefly gained attention for his bold policy proposals and overconfidence, has withdrawn from the race for the Republican White House nomination following a disappointing fourth-place finish in the Iowa caucuses.

Expressing regret over not delivering the anticipated surprise, Ramaswamy endorsed former President Donald J. Trump for the White House during a statement in Des Moines on Monday night. Despite initially being an unlikely contender, Ramaswamy closely aligned himself with Trump, pledging support even in the face of potential legal issues and promising a pardon if elected.

However, just two days before the Iowa caucuses, Trump's campaign turned against Ramaswamy, labeling him a fraud and urging voters to reject him. This marked a shift from months of warmth between the two figures.

As the Harvard-educated Ramaswamy continued his campaign, he embraced apocalyptic conspiracy theories, alleged a "system" blocking Trump's return to office, and propagated the unfounded theory of "replacement," falsely claiming Democrats aimed to replace white people with immigrants of color.

Ramaswamy's opening strategy emphasized his superior understanding of the Constitution and civil service laws, promising to take Trump's America First agenda even further. This included executive orders to immediately eliminate the Department of Education, F.B.I., and Internal Revenue Service, a 75 percent reduction in the federal workforce through mass layoffs without congressional approval, and scaling back foreign military commitments.