Former Vice President Joe Biden says he has “pretty profound differences” with some of his top rivals for the Democratic presidential nomination race over the costs and consequences of Medicare for All.

Biden, the current front-runner in the nomination battle, appeared on Friday evening to take a jab at Sen. Kamala Harris of California over a lack of straightforwardness on her support for Medicare for All. At the same time, he singled out Sen. Bernie Sanders for being honest about the ramifications of implementing the single-payer healthcare plan.

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"Bernie's been very honest about it. He said you're going to have to raise taxes on the middle class. He said it's going to end all private insurance. I mean, he's been straightforward about it. And he's making his case," Biden said after an impromptu gaggle with reporters following a stop at an ice cream shop in New Hampshire, the state that holds the first primary in the White House race.

Sanders, the independent senator from Vermont who’s making his second straight bid for the Democratic nomination, has long pushed for Medicare for All. Sanders touts that under his proposal, premiums, co-payments and out-of-pocket expenses would be eliminated, but admits that taxes would increase.

Biden is the only one of the top contenders who opposes the plan, in which all Americans would obtain their health insurance from a government operated program like Medicare.

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When asked if other Democratic White House hopefuls are as straightforward about their support for the single-payer system, the former vice president answered, "well, so far, not. So far, not. They may.”

Asked specifically by reporters if Harris has been honest about whether her version of Medicare for All would end private insurance, Biden answered, "I'll let you guys make that judgment."

Harris has said her plan would allow private insurance to continue to exist. But during last month’s first round of presidential primary debates, she raised her hand when the candidates were asked whether – if elected – they would eliminate private insurance. She later explained that she had misheard the question.

In the pivotal moment of that debate, Harris went on the attack against Biden, as she criticized recent comments by the former vice president spotlighting his ability to find common ground during the 1970s with segregationist senators with whom he disagreed, and over his opposition decades ago to federally mandated school busing.

Harris has seen her poll numbers soar in the wake of that nationally televised showdown, while Biden’s once big lead in the national and early primary and caucus voting state surveys has started to slip.

At those debates, Sen. Elizabeth Warren of Massachusetts showcased her strong support for Medicare for All. Warren, along with Harris and two more White House contenders – Sens. Cory Booker of New Jersey and Kirsten Gillibrand of New York – co-sponsored the 2017 Medicare for All bill introduced by Sanders.

But Biden has issues with the plan.

"I'm not saying that people will necessarily vote against it," he told reporters.

But he added: “I think it gets hard to explain it and indicate how you're going to be OK; there's going to be nothing missing, as my mother would say, between the cup and the lip."

Earlier, at a campaign event in nearby Dover, New Hampshire, Biden emphasized he would prefer to keep the Affordable Care Act, better known as Obamacare, but expand it by giving people an option to buy into a Medicare-like program.

“Keep Obamacare. Restore the cuts that have been made, and add a public option,” he said to applause. “If you like your employer insurance, you get to keep it.”

Biden, who served eight years as President Barack Obama’s vice president, infamously called Obamacare a “big f—king deal” during the bill’s White House signing ceremony in 2010.

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Congressional Republicans for years tried unsuccessfully to repeal the government health care program. But Obamacare’s been severely weakened since GOP President Donald Trump succeeded Obama in the White House.