Gov. Scott Walker of Wisconsin has concluded he no longer has a path to the Republican presidential nomination and plans to drop out of the 2016 campaign, according to three Republicans familiar with his decision, who spoke on condition of anonymity.

Mr. Walker called a news conference in Madison at 6 p.m. Eastern time.

“The short answer is money,” said a supporter of Mr. Walker’s who was briefed on the decision. “He’s made a decision not to limp into Iowa.”

Mr. Walker’s intended withdrawal is a humiliating climb down for a Republican governor once seen as all but politically invincible. He started the year at the top of the polls but has seen his position gradually deteriorate, amid the rise of Donald J. Trump’s populist campaign and repeated missteps by Mr. Walker himself.

In the most recent CNN survey, Mr. Walker drew support nationally from less than one-half of one percent of Republican primary voters. He faced growing pressure to shake up his campaign staff, a step he was loath to take, according to Republicans briefed on his deliberations.