Over the first two nights of the Democratic convention, Republicans who support former vice president Joe Biden have had about as prominent a role as the party’s young, more liberal voices.

Rep. Alexandria Ocasio-Cortez (D-N.Y.), unquestionably the most famous and popular Democratic politician under the age of 50, got about a minute and a half to speak Tuesday, a minute less than former secretary of state Colin Powell. Earlier, a group of more than a dozen young Democratic officials gave a Voltronesque keynote that extended for about 13 minutes; the night prior, four Republican elected officials spoke for about half that duration.

For young Democrats, it’s baffling. Why focus on former governor John Kasich (R-Ohio) instead of inspiring young voters by giving Ocasio-Cortez a bigger role? At its heart, though, this friction reflects a central question the party faces in its efforts to oust President Trump. Is it a better use of time to try to encourage Trump voters to swing toward Biden? Or should they instead encourage voters who stayed home four years ago to go to the polls?

Considering only the results of the last presidential contest, it’s hard in the abstract to determine which focus makes more sense as a priority. It was so close in the three states that determined the outcome that a number of changes might have made a difference.

An analysis of the 2016 electorate completed by a group of researchers in 2018 offers insight through the lens of voters who cast ballots for President Barack Obama in 2012. Had the 2016 vote precisely mirrored the 2012 vote, of course, Trump would have lost. But about 20 percent of those who supported Obama in 2012 didn’t vote for Hillary Clinton four years later.

Some, about 3.5 percent of the total, backed third-party candidates. About twice as many simply didn’t vote. A bit under half flipped, voting for Trump.

Those last two groups are the ones that reflect the debate outlined above. About 4.4 million Obama voters didn’t vote. About 6 million flipped from Obama to Trump. Which should be the party’s priority?

That research, provided to The Post at the time, shows central differences between the groups that offer insight into the shifts.

For example, about 16 percent of those who voted for Obama in 2012 and Trump in 2016 were non-White, compared with more than half of those who stayed home.

Over a third of those who voted for Obama in 2012 but didn’t vote in 2016 were Black. The analysis suggests that about 1 in 9 of Black Obama voters in 2012 stayed home. About 1 in 9 White 2012 Obama voters flipped to support Trump.

The plurality of those Obama-Trump voters were Republican. Some 2.3 million Republicans voted for Obama in 2012 and Trump in 2016, according to this analysis. Hence the Kasich and Powell appearances, an attempt to convince that group and others like them to switch once again.

More important to the question is the ease with which the campaign can accomplish its desired outcome. In other words, is it easier to convince a Trump voter to vote for Biden, or is it easier to get a likely Biden voter to go to the polls?

In 2017, I spoke with Zach Silk, president of Civic Ventures and a former manager of congressional and ballot initiative campaigns, to assess this particular question. When we spoke, Democrats had narrowly lost a special election in Georgia’s 6th Congressional District.

“We now know, I think pretty conclusively, that in general, politics is more partisan,” Silk said of the effort to convince Republicans to back the Democratic candidate. “The number of persuadable voters is fewer than ever before. And so the amount of just raw energy and money that is spent on persuasion is probably disproportionate to those who can be persuadable, relative to other periods of modern campaign history.”

In other words, doing the sort of persuasion needed to get a Republican to consider Biden is difficult. But, Silk said, it was still the easier option.

On the Democratic National Convention's first night, former Ohio governor John Kasich (R) urged Republicans to support Democratic nominee Joe Biden. (The Washington Post)

“The people who are obsessed with … turning out low- — low-frequency voters, you know, it really is very difficult to turn them out,” he said. “And the amount, the intense amount of engagement that you have to have with those voters — it’s been proven both empirically in political science research, as well as if you talk to anybody who’s worked a modern field program: It’s extraordinarily difficult to turn them out.”

It’s generally akin to what marketers experience in trying to sell products. It’s easier to sell to existing customers than to new ones. It’s similarly easier to get someone to cast a particular vote than to vote at all.

What’s more, the benefit of getting someone to flip her vote is twice the benefit seen in simply getting her to vote. Consider a race in which Candidates A and B are each supported by 100 voters. If Candidate A manages to turn out one more vote, the total becomes 101 to 100. But if Candidate B manages to flip a supporter of his opponent, A loses a vote, and B gains one — a shift of two votes.

Those 2012 Obama voters who didn’t vote in 2016 were disproportionately members of groups that turn out less heavily. Nearly a quarter were under the age of 30, for example, a group that’s less likely to vote for a wide range of reasons, including that they are more likely to have moved since the last election and less likely to have the flexibility needed to make time to vote. As Silk explained when we spoke, voting is also a habit, and the younger you are, the less likely you are to have built that habit into your routine.

None of this necessarily means that the Democratic Party’s time is better spent on convincing Republicans to back Biden than on getting infrequent voters to cast a ballot. The party will have a slew of opinions and polling to guide that balance.

That so much time has been spent making the case to Republicans, though, suggests what that research probably says.