The 2020 presidential race is heating up, and candidates are starting to jockey for position. One high-profile entry into the race came last week, when Sen. Bernie Sanders, I-Vt., announced his plans to make another run for the White House for next year's elections.

One issue that became particularly controversial during the 2016 election was the release of tax returns. President Trump chose not to disclose his tax return information during the campaign, raising questions about what information those returns might include that could be problematic for the candidate. That issue has come to the forefront again recently, with some candidates having chosen to release several years' worth of returns and calling on others to follow suit. Sanders has been somewhat reticent about his tax information, and despite an increase number of calls for him to join others who've been forthcoming, the only tax return on record for Sanders is his 2014 return.

Below, we'll look at those returns and highlight some of their most important aspects.

Tax forms with glasses, calculator, pen, and $100 bills.

Image source: Getty Images.

1. The Sanders family largely lived off his Senate salary

Nearly all of Sanders' income comes from his work as an elected official. The senator reported wage income of $156,441 in 2014, which matches up reasonably well with the official gross pay of $174,000 for the Senate that year.

It's typical for reported wages to be less than gross salary. Deductions like health insurance payments, employer-sponsored retirement plan contributions, and flexible spending arrangement contributions that get withheld directly from pay are typically excluded from wage income, and W-2 forms routinely list the net amount for taxpayers to include. With wages having stayed at $174,000, it's likely that Sanders wouldn't have seen much change in this number on more recent returns.

2. Sanders collects Social Security -- and it's subject to income tax

The Sanders household is one of millions that has to pay taxes on Social Security benefits. Because the family's income is well above the $44,000 threshold for married couples, Sanders had to include 85% of the $46,213 in Social Security benefits the family received as taxable income.

Also, $46,213 might seem like a lot of Social Security, working out to $3,851 per month. But keep in mind that the amount includes benefits for both Sanders and his spouse, and so while it reflects healthy income levels over the course of a long career, it's far from the maximum amount a family could get from Social Security.

3. Sanders' deductions are largely unremarkable...

Like many Americans, the Sanders household itemized deductions in 2014. The two items he claimed that had the biggest impact on his return were two very popular deductions: home mortgage interest and state and local taxes.

Sanders paid $22,946 in deductible home mortgage interest, and real estate taxes on his property amounted to another $14,843. Add in $9,666 paid for state income taxes and $8,350 for charitable contributions, and you have the bulk of the deductions that the tax return claimed. Sanders is also one of many who'll be affected by the 2018 limitation on state and local taxes to $10,000, with a potential reduction of more than $14,500 in allowable itemized deductions on that front.

4. ... But one deduction was noteworthy

More unusual was a very small deduction Sanders took. The senator claimed $4,473 in unreimbursed employee expenses, all attributable to meals and entertainment that he ascribed to his work. Tax law typically allows 50% of the cost of business-related meals to be deductible, as long as a business discussion occurs.

What makes the deduction so interesting is that because it's a miscellaneous itemized deduction, it's only deductible to the extent that it exceeds 2% of adjusted gross income. Because Sanders' AGI was $205,271, only $572 of his miscellaneous deductions were actually deductible.

5. What the Sanders household paid in taxes -- and got as a refund

Overall, Sanders claimed taxes of $27,653 on his family's 2014 return. With $31,825 withheld from his Senate pay, that gave the senator a refund of $4,172 that year.

Taxes of $27,653 on adjusted gross income of $205,271 amount to an effective tax rate of about 13.5%. That shows the importance of itemized deductions for helping higher-income taxpayers reduce their tax rate.

What to expect from Sanders' later tax returns

When Sanders decides to release more recent tax returns, the public will get a better sense of how typical 2014 was for his household from a tax perspective. According to other financial disclosures, the Sanders household's income rose dramatically in the years since his last disclosed tax return, with book proceeds potentially adding to taxable income depending on whether Sanders donated them to charity.

For now, though, Sanders has elected only to disclose this one return. Until he agrees to be more forthcoming, campaign watchers will have to use other sources to try to draw out information about the presidential candidate's finances.