(CNN) Everyone knows that how the Senate's impeachment trial plays out will have an effect on President Donald Trump's reelection bid this November -- and, maybe, on who Democrats nominate to take him on.

What's less known, or at least covered, are the ways in which the ongoing impeachment trial could dramatically effect Democrats' effort to retake the Senate majority this fall.

First, the numbers. Republicans have a 53 to 47-seat edge over Democrats at the moment. (Technically, Sens. Angus King of Maine and Bernie Sanders of Vermont are independents but both caucus with Democrats.) Which means that Democrats need to net three seats to win the majority if they also win the White House and four seats if their side comes up short in the presidential election again. (The vice president breaks ties in the Senate, giving whichever party controls the White House effective control over a 50-50 Senate.)

In the 2020 election, Republicans have to defend 23 seats , compared to just 12 for Democrats. (The 2014 election cycle was a very good one for Republicans.)

That discrepancy in seats led to some early optimism for Democrats, who believe that a credible path exists for them to seize back the majority they lost in the 2014 election. And as the election cycle has matured, that initial assessment has proven generally correct -- with most nonpartisan political handicappers agreeing that the Senate is in play.

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