Days after he admitted that he would consider dropping out of the 2016 White House race if his polls dipped, Donald Trump may be falling victim to a self-fulfilling prophecy as his numbers are slipping in key early-voting states.

The Republican front-runner's lead in New Hampshire, which had expanded to an impressive 16 percentage point last month, was down to 5 points this time around, based on a new NBC News/Wall Street Journal poll. Trump also lost two percentage points in Iowa, which traditionally kicks off the nomination calendar with its caucuses, the newspaper added.

In the Granite State, which holds the first-in-the-nation primaries, the real-estate tycoon now garners the backing of 21 percent of Republicans.

He is trailed by former Hewlett-Packard chief executive Carly Fiorina, who logged 16 percent, as well as former Florida Gov. Jeb Bush (11 percent); Florida Sen. Rubio and retired neurosurgeon Ben Carson (tied at 10 percent); New Jersey Gov. Chris Christie (7 percent); and Texas Sen. Ted Cruz and Ohio Gov. John Kasich (tied at 6 percent).

In the Hawkeye State, meanwhile, Trump is backed by 24 percent, followed by Carson (19 percent), Fiorina (8 percent) and Bush (7 percent), as well as Cruz, Rubio and Louisiana Gov. Bobby Jindal (all tied at 6 percent).

Both surveys were conducted between Sept. 23 and Sept. 30 among 431 potential Iowa caucus-goers and 450 potential New Hampshire primary voters, all of them GOP supporters, NBC News detailed. The margins of error came to plus or minus 5.3 percentage points in Granite State poll, and plus or minus 4.6 percentage points in the Hawkeye State survey, respectively.

Trump had told CNBC's John Harwood last week that he would abandon his presidential campaign if his poll numbers started to drop significantly, the Hill recalled.

"Right now I'm leading every poll -- and in most cases big. And I'm leading Iowa, I'm leading New Hampshire, I'm leading South Carolina, I'm leading everything," he said.

"(But) if that changed -- if I was like some of these people at 1 percent and 2 percent, there's no reason to continue forward."