►Socialism. Sen. Bernie Sanders' definition of socialism poses no threat whatsoever to Americans or our democracy. Yet, the word has become so toxic, so bastardized, so perfectly suited to President Donald Trump's negative sloganeering, that the 2020 election could hinge on a single word. Mix in the ill-timed posturing of four progressive congresswomen known as The Squad, and you have a situation that is perplexing Democrats and uniting conservatives.

►Health care. It's an issue on which Democrats should score handily. Yet, one wrinkle in so-called Medicare for All, authored by Sanders and embraced by several other candidates -- that Americans would lose their current private coverage even if they like it -- is polluting the discussion. Republicans have no plan, but now they have a fear-based attack theme: Socialists want to take away your medical insurance.

►Economy. Defeating an incumbent president is difficult, and ousting one during a period of ultra-low unemployment and a thriving stock market is even harder. However, Democrats have a compelling case to make: Wages remain low, Trump's tax schemes have disproportionately benefited the wealthy, and his approach to international trade is likely to disrupt and damage the American economy in the long run. Plus he's driving up the debt. But it's asking a lot of voters to see this financial forest given there are so many seemingly healthy trees.

►Age. This is 2020's X factor. We've come to understand that elected officials, along with Supreme Court justices, can serve effectively into their 70s and even 80s. The problem for Democrats isn't the actual age of their leading candidates, per se, it's how these people "play," as Hollywood would put it. Donald Trump (74 at the next Inauguration Day) comes off as being more energetic and alert than Joe Biden (who would be 78).

I have no way of knowing how mentally dexterous Biden is, but what I see isn't reassuring. He continues to fumble on the trail as he did in the first debate, prompting concern that this condition will worsen with, yes, age. Sanders and Sen. Elizabeth Warren seem spry, but in January 2021 he'll be 79 and she'll be 71.

The debates in Detroit, July 30 and 31 on CNN, might provide some clarity. Sanders and Warren will likely dominate the first night, but can they separate themselves philosophically while also deflecting criticism of the "socialist" agenda? The following night Biden will find himself wedged -- figuratively as well as physically -- between Sens. Kamala Harris and Cory Booker. Both have stepped up criticism of Biden's record on racial issues.

Harris essentially doubled her standing in the polls following the June debates and she raised $12 million in the second quarter. But that was less than half of what South Bend, Indiana Mayor Pete Buttigieg collected. In fact, among those giving $200 or more, Buttigieg outperformed Harris in her home state of California -- not a good sign.

The debates could provide what golfers call "moving day" up the leaderboard for candidates I found to be impressive on the ground in Iowa: Buttigieg, Sens. Michael Bennet and Amy Klobuchar, and former Housing and Urban Development Secretary Julian Castro. However, with 10 competitors on the stage each night, it won't be easy.

If Harris can pull off another strong debate performance, she will be hard to dismiss. But at campaign appearances, I found her soft on some subjects and equivocal on certain questions.

At this point, Democrats seem to be grooming a better crop of potential vice presidential candidates than ticket-toppers. Bennet, Booker, Klobuchar, Harris and Castro would each make splendid running mates if paired with the proper presidential nominee. Of course, no one runs for veep so far ahead of the first voting in February -- or, at least no one dares to admit it.

Donald Trump is arguably the worst president, and the most dangerous, in U.S. history. He should be planning his retirement at Mar-a-Lago or Leavenworth rather than taking any comfort in speculation about another Electoral College victory. The right opponent should clean his clock.

Yet, looking at the Democrats' field of 25 presidential aspirants, what comes to mind is Casey Stengel's query as he surveyed the players on his 1962 Mets: "Can't anybody here play this game?"

(c) Peter Funt. This column originally appeared in USA Today.