Taxes. They're an inevitable reality for working Americans; one of the two certainties in life, an often-repeated quote attributed to the Founding Father Benjamin Franklin tells us.

And they're a subject that President Donald Trump cannot shake: He famously never released his tax returns prior to being elected to the nation's highest office, breaking a 46-year-old tradition, and he along with a Republican-controlled Congress passed a major tax bill in 2017 — one of his campaign promises.

The all-things-taxes scrutiny is also ratcheting up now that the 2020 election season has begun. Democratic candidates vying for the nomination are doing what Trump has not: making their tax returns available to the public.

Candidates are also offering a different system, where the wealthiest people and corporations would pay higher taxes in order to fund other programs. Sen. Bernie Sanders is one of those candidates and he offered his ideas to Fox News viewers on Monday night.

On Tuesday, Trump tweeted his response.

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Taxes. They're an inevitable reality for working Americans; one of the two certainties in life, an often-repeated quote attributed to the Founding Father Benjamin Franklin tells us.

And they're a subject that President Donald Trump cannot shake: He famously never released his tax returns prior to being elected to the nation's highest office (breaking a 46-year-old tradition), and he along with a Republican-controlled Congress passed a major tax bill in 2017.

Questions about Trump's taxes have only intensified since his election. Democratic lawmakers, who now control the House of Representatives, have issued subpoenas for documents related to several ongoing investigations, including asking for Trump's financial information.

On Monday, the Financial Services Committee requested records from Deutsche Bank, and last week the House Ways and Means committee extended its deadline for the IRS to turn Trump's tax returns over to the committee (after the Treasury said it would miss the initial April 10 deadline).

And given that tax day just passed this week — the first one with Trump's new tax law in place — the Tax Cuts and Jobs Act of 2017 is still being scrutinized. (And according to Politico, they are "deeply unpopular.")

The tax scrutiny is also ratcheting up now that the 2020 election season has begun. Democratic candidates vying for the nomination are doing what Trump has not. They are making their own tax returns public.

Sen. Kamala Harris released 15 years of returns over the weekend, former Rep. Beto O'Rourke published 10-year's worth on Monday, as did Sen. Bernie Sanders, after not releasing his tax returns during the 2016 election.

Several Democratic candidates are also proposing a different tax system, one where the wealthiest 1% or corporations pay more so that programs like Medicare for All can be funded. For example, Sen. Elizabeth Warren of Massachusetts proposed a wealth tax that would impose a fee on one's cumulative net worth, in addition to the tax on regular income they earned for the year, according to The New York Times.

Sen. Sanders offered his vision for a new taxation system during a Fox News town hall on Monday. He also discussed his newly-released returns and called out Trump on both the tax law and his still-unreleased tax returns.

"I pay the taxes that I owe." Sanders said. "And by the way, why don't you get Donald Trump up here and ask him how much he pays in taxes."

Sanders' returns revealed that he and his wife made more than $1 million in 2017 and in 2016, and therefore plopping him in the IRS's top 1% bracket, The New York Times reported, meaning he pays 26%. Sanders made waves in 2016 for railing against "millionaires and billionaires." He has explained his increase in revenue by pointing to his best-selling book.

During the town hall, Sanders called the tax system "absurd" and criticized major corporations that don't pay federal taxes.

"We have an absurd tax system, and while millions of people today are paying actually more in taxes than anticipated, Amazon, Netflix, and dozens of major corporations, as a result of Trump's tax bill, paid nothing in federal taxes," Sanders said. "I think that's a disgrace."

On Tuesday night, a day after the Fox News town hall, Trump tweeted his response.

"Bernie Sanders and wife should pay the Pre-Trump Taxes on their almost $600,000 in income. He is always complaining about these big TAX CUTS, except when it benefits him," he said. "They made a fortune off of Trump, but so did everyone else - and that's a good thing, not a bad thing!"

"I believe it will be Crazy Bernie Sanders vs. Sleepy Joe Biden as the two finalists to run against maybe the best Economy in the history of our Country (and MANY other great things)!" he continued. "I look forward to facing whoever it may be. May God Rest Their Soul!"

Trump also tweeted frustration with Fox News, a network he usually reserves for praise, apparently for having hosted Sanders, saying in part, "What's with @FoxNews?"

Sanders quipped back over social media: "Looks like President Trump is scared of our campaign. He should be."