Marco Rubio. REUTERS/Brian Snyder Earlier this spring, Sen. Marco Rubio's (R-Florida) pollster publicly laid out a potentially harsh truth: By his calculations, the eventual Republican nominee would need to capture 40% of the Latino vote in order to win in 2016.

“Un­less you count on the Re­pub­lic­an getting Ron­ald Re­agan-like num­bers among whites, you’re go­ing to have to be some­where in the mid-forties with Hispanics,” Whit Ayres said, according to the National Journal.

Though somewhat shocking in its candor — former Massachusetts Gov. Mitt Romney (R) carried just 23% of the Latino vote in 2012 — Ayres' comment emphasized what the Republican establishment has known for some time.

In a now infamous Republican "autopsy" report after the 2012 election, the Republican National Committee declared that the party needed to make significant inroads among Latinos — one of the largest and fastest-growing demographics in the US — if it hoped to be competitive in future elections. The party's standing with the bloc had crumbled since President George W. Bush carried 44% of the Latino vote in 2004.

But now, with Latinos rebuking Republican presidential front-runner Donald Trump's inflammatory comments about immigrants, the goal appears further from reach.

Indeed, an extensive new report from the left-leaning Center for American Progress (CAP) lays out just how steep a climb the Republican nominee will face next November.

'The eventual Democratic nominee ... is likely to have significantly more voters from communities of color to work with.'

The report notes that even by modest standards, Democrats have a significant, though not unbeatable, advantage heading into the 2016 election, primarily because of the growth of a diverse coalition of voters that backed President Barack Obama in 2012 — millennials, Latinos, and single women.

White voters remain a solidly Republican bloc, though Democrats have gained with white single women and college-educated white voters. Married and working-class white voters continue to gravitate toward the Republican Party, according to the report.

While the share of white voters is expected to shrink two percentage points lower than its level in 2012, the share of young and minority voters will likely be two points higher that it was in 2012. CAP suggested that the number may be even higher in key swing states.

"The eventual Democratic nominee is therefore likely to have significantly more voters from communities of color to work with in 2016 than in 2012," said the report, which was authored by Ruy Teixeira, John Halpin, and Rob Griffin. "But can she or he plausibly hope to replicate the 81% support among these minority voters President Obama received in his 2008 and 2012 election victories?"

Even in somewhat dire election outcomes, Democrats have the upper hand

If the eventual Democratic nominee maintains 2012 levels of support among three key groups — an "11-point deficit among white college graduates, a 22-point deficit among white working-class voters, and a 64-point advantage among minority voters" — the Democratic candidate will overwhelmingly win the popular vote, and will almost certainly win the election, the report's authors concluded.

And even though minority voters, who are expected to make up 30% of the electorate in 2016, are key to Democrats' election strategy, the nominee could actually afford to lose some support within those blocs.

CAP estimated that even if minority groups' support for the Democratic nominee fell to 78%, and if opposition among white working-class supporters stood at the levels of the 2014 midterm elections, in which Democrats were crushed, Democrats could still win if the party maintained its 2012 support from white college graduates.

Donald Trump. AP Photo/Charlie Neibergall

'The Republican Party will be defined by the candidate who wins the nomination, not the candidates who lost'

The path for a Republican nominee to win the presidency relies on the party continuing to make sweeping gains among white voters.

Here's a theoretical scenario in which Republicans could win the popular vote, according to CAP: Democrats would capture just 78% of the minority vote — again, a three-point decline from 2012. And support among white college-graduate Democratic voters would deflate to match levels of the 2014 midterm elections, a disastrous cycle for Democrats.

But it's not clear if such a breakdown would help the eventual Republican nominee in key swing states. Moreover, turnout among Democratic voters is consistently better during presidential elections and drops sharply during midterms.

Despite the seemingly inevitable longer-term demographic problems for Republicans, some commentators and party strategists have argued that, at least for the time being, expanding gains among white voters could propel the GOP to the White House in 2016.

Sean Trende, an analyst at Real Clear Politics, has posited that another path to a GOP victory is by tapping into a pool of "missing" white voters who were unmoved by Romney in 2012. The theory goes: If Republicans can motivate more white voters, and minority voters show up at lower levels without Obama on the ballot, Republicans could narrowly take back the White House in 2016.

But as the National Journal notes, the problem with this theory is that white voters continue to make up a smaller share of the electorate. Non-college-educated white voters and married white voters, both groups that have been increasingly likely to vote, have all represented a shrinking share of the electorate over the last several elections. But the challenge for Republicans is motivating millions of "disenchanted" voters who stayed home in 2012 to suddenly show up.

The main challenge for Democrats is that voters appear less enthused about the 2016 election than Republican voters.

As Slate's Jim Newell has noted, a recent survey from the Democratic firm Greenberg Quinlan Rosner found that young and minority voters are less interested in the 2016 election at this point, compared to white voters.

This so-called enthusiasm gap has raised eyebrows in former Secretary of State Hillary Clinton's campaign, which is already rolling out targeted plans to reach out to groups like Latino voters in contested states like Nevada. But some party insiders have maintained an air of nonchalance about the perceived problem, since the election remains nearly a year away.

For their part, though many Republicans have become more concerned that increasingly inflammatory rhetoric is damaging the party's chances at the White House; others believe such talk could quickly be forgotten in a general election.

When asked whether Rubio could meet the 40% threshold that his pollster had thrown out, one party insider predicted he would.

"The Republican Party will be defined by the candidate who wins the nomination, not the candidates who lost," the official told Business Insider.