Sen. Marco Rubio (R-Fla.) came in fourth among Republican presidential candidates in a recent poll, trailing leader Donald Trump and second-place Jeb Bush by double-digits. That would be discouraging enough for Rubio’s campaign if it was a national survey. What makes it even worse is that the poll was of voters in Rubio’s home state of Florida.

To be fair to Rubio, the survey, conducted by St. Pete Polls, was an “email opt-in poll,” a method of unknown reliability. But in another Florida poll released by Mason-Dixon on Friday, Rubio trailed Bush by 12 points, with Scott Walker and Trump not far behind him. In Mason-Dixon’s previous Florida poll, Rubio was essentially tied with Bush.

Not so long ago, many saw the Florida senator as a “front-runner” for the Republican nomination. His youth would let Republicans turn a matchup with Clinton into “the future vs. the past,” and his moderate stance on immigration would neutralize Democrats’ strength with the growing Hispanic vote. After announcing his campaign in April, Rubio vaulted into the top tier in nationwide polls for several weeks. But whatever bump he got out of the announcement has evaporated: In RealClearPolitics’ poll average, Rubio is now just above 7 percent — exactly where he was before his campaign officially began. In the money race, his numbers are a little stronger, but some of his key rivals either didn’t officially launch their campaigns and fundraising until recently (Walker) or don’t really need to raise funds (Trump).

What happened? While it would be tempting to pick one big cause, Rubio’s stumble is probably due to a combination of factors: his stumbling answer on the Iraq war, his continued moderation on immigration (an anathema to many GOP voters) and, most recently, Trump’s entrance into the race. Perhaps the biggest problem is that while he is acceptable to many parts of the GOP base, he is none of those parts’ first choice.

In one sense, Rubio has no weakness so big that he can’t recover in the polls, and there are plenty of upcoming debates to make his case. But where exactly is he supposed to break through? Iowa? Rubio is eighth there. New Hampshire? He’s fourth there, much closer to also-rans such as Rand Paul and Ted Cruz than to Bush, Trump or Walker. His campaign is touting “backing in states often ignored by presidential candidates” and “quiet trips” to South Carolina (where he also trails badly) — storylines campaigns push only if there are no good poll numbers in early states to promote. Unless things change soon, the one-time GOP front-runner will be a mere footnote in the 2016 campaign.