Hillary Clinton should find ways to bolster her former boss’ public approval ratings, because it will be hard, if not impossible, for her to finally win the Oval Office if President Obama doesn’t reach a consistent 50 percent by Election Day 2016, according to an analysis of 62 years of polling and election data.

Even more than the popularity of candidates running for office, the incumbent president’s approval rating “explains over half of the variance in the vote share of his party’s nominee,” said the analysis by the University of Virginia’s Center for Politics.