Vermont Sen. Bernie Sanders criticized his 2020 presidential rival Sen. Elizabeth Warren's funding plan for "Medicare For All," calling his plan "more progressive" and squaring up the two most progressive candidates in the race for the Democratic nomination to do what neither of them have wanted to do: draw distinctions between each other.

Sanders, who has centered his candidacy around the fight for his single-payer Medicare for All legislation, told ABC News in an interview published Sunday that although he and Warren believe everyone should have health care, they differ on how to fund it. Her plan, he also said, would "have a very negative impact on creating jobs."

"We do disagree on how you fund it," Sanders told ABC News. "I think the approach that (I) have, in fact, will be much more progressive in terms of protecting the financial well being of middle income families."

Sanders specifically criticized the Massachusetts senator's nearly $9 trillion tax on employers. "I think that that would probably have a very negative impact on creating those jobs," Sanders said of the tax Warren's plan calls an "employer Medicare contribution." "Or providing wages, increased wages and benefits for those workers."

President Donald Trump says he is particularly pleased with the jobs created during his three years in office. "We're producing jobs like you have never seen before in this country," he said during a recent speech in Michigan.

But you don't have to go back far to find three years of better job growth. Just to back to the previous three years under Barack Obama.

During Trump's first 36 months in office, the US economy has gained 6.6 million jobs. But during a comparable 36-month period at the end of Obama's tenure, employers added 8.1 million jobs, or 23% more than what has been added since Trump took office.

The average monthly gain so far under Trump is 182,000 jobs. During the last 36 months under Obama, employers were adding an average of 224,000 jobs a month.

Senator Bernie Sanders pushed back to clarify his position on immigration on Sunday after he was asked in Iowa about his reported support for open borders.

"I'm afraid you may be getting your information wrong," said Sanders, an independent from Vermont who is currently seeking the Democratic nomination to unseat President Donald Trump in 2020, The Washington Post reported. "I think what we need is comprehensive immigration reform," he said.

"Oh my god, there's a lot of poverty in this world, and you're going to have people from all over the world. And I don't think that's something that we can do at this point. Can't do it," the senator added.

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Some immigration advocates and progressives have pushed for open borders, however, and many were quick to criticize Sanders's response on social media. Many said he sounded like Trump on immigration, while others argued that the U.S., as a wealthy nation, should show more concern about the plight of migrants.

Coping with the Demographic Challenge: Fewer Children and Living Longer (Social Security Bulletin, Vol. 66, No. 4, 2005/2006)

Due to demographic changes, the U.S. Social Security system will face financial challenges in the near future. Declining fertility rates and increasing life expectancies are causing the U.S. population to age. Today 12 percent of the total population is aged 65 or older, but by 2080, it will be 23 percent. At the same time, the working-age population is shrinking from 60 percent today to a projected 54 percent in 2080. Consequently, the Social Security system is experiencing a declining worker-to-beneficiary ratio, which will fall from 3.3 in 2005 to 2.1 in 2040 (the year in which the Social Security trust fund is projected to be exhausted). This presents a significant challenge to policymakers.

One policy option that could help keep the Social Security system solvent is to reduce retirement benefits, either by raising the normal retirement age or through life expectancy indexing, to reflect the fact that people are living longer. However, these reductions in benefits have the potential to harm economically vulnerable retirees. Other options, such as progressive price indexing proposals, explicitly protect the retirement benefits of low lifetime earners. Still other options would seek to raise additional revenue for the system.

Since individuals will be living longer in retirement, many policymakers believe it is important to encourage older workers to delay retirement so that they can maintain a quality standard of living throughout their retirement. One proposal to encourage continued work would be to increase the early eligibility age for Social Security benefits from age 62 to age 65. This could possibly hurt individuals who need to retire from physically demanding jobs but would ensure that people receive higher benefit amounts once they were able to fully retire.

Other proposals that could promote more work at older ages include expanding phased retirement options and reforming pension and defined contribution systems to create incentives to work and save.

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Immigration also plays a role in the age structure of the population. Compared with earlier decades, net immigration has increased in recent years (Table 2). Because immigrants tend to be younger and have higher fertility rates than the general population, immigration mitigates the aging of the population. Without immigration the aging trend would be more pronounced.