Republican presidential candidate Donald Trump conceded Tuesday that his campaign's voter turnout effort in Iowa was less robust than that of other campaigns, one day after finishing behind Sen. Ted Cruz (Tex.) in the caucuses.

"We didn’t have much of a ground game because I didn’t think I was going to be winning,” Trump said on Fox News Tuesday. “That’s why I’m so honored to have come in second. Most people said I wouldn’t be in the top 10 originally when I started in Iowa."

"And yeah, in retrospect, we could have done much better with the ground game, yes," he added.

The campaign was frequently criticized in the run-up to the election by Iowa operatives who said Trump’s team had not invested in a strong infrastructure in the state. Trump's campaign downplayed that scrutiny at the time, even as attention turned to the Cruz team's laser-like focus on voter outreach and turnout. The caucuses Monday were the first test of Trump's ability to translate the energy fueling his candidacy into something more tangible: votes.

The billionaire showman stressed Tuesday that Cruz and other candidates spent more money in Iowa than he did, retroactively lowering expectations after weeks of remaining bullish about his chances of coming in first place.

Trump added that he believes his campaign is in strong shape ahead of the Feb. 9 New Hampshire primary, which he called a "natural fit."

“You know, if you just take a look at the overall picture, here I'm doing so well. It's a very natural fit,” he said, speaking remotely from New Hampshire. “I've known the people for years. I've been up in New Hampshire for years. I love the place, and I think I'm going to do great here."

Republican presidential candidate Donald Trump spoke in front of a crowd in Iowa following the caucuses. Trump finished second to Ted Cruz. (Reuters)

Trump gave a short concession speech Monday evening at the Sheraton in West Des Moines, where he congratulated his opponents but remained focused on the upcoming primary in the Granite State, where he is leading by a wide margin. Trump said that the primary system in New Hampshire is simpler than the caucus system in Iowa, indicating that the system could benefit him.

“It’s a different system. But [caucusing] is a very complex system. And for tabulating votes and for, you know, going through a whole process, it makes it certainly much more difficult,” he said. “I must say, I think that the good old simple system where you walk in and you cast your vote, like we have, as an example, in New Hampshire, I think it’s better.”

“Simpler, better, more direct,” he said. “But the caucus system, it does serve a purpose. And I understand it very well.”