With three weeks to go until the Pennsylvania primary, Former Secretary of State and First Lady Hillary Clinton stands about 22 points ahead of her challenger, US Senator Bernie Sanders. That number is the latest according to a Harper Polling Survey of 603 likely Democratic voters that was released on Tuesday. Clinton’s support sits at 55%, while Sanders’ share of voters is at 33%.

There are several complicating qualifiers to this data, however. Everything isn’t all bad news for Sanders; it just underscores the tough battle being waged by his campaign.

When looking at the Harper Polling data trend since the beginning of 2016, Sanders is the only one actually increasing support, although his increase barely exits the margin that could be explained by the margin of error, which, for this study, is 4%. (Margin of error refers to “an amount that is allowed for in case of miscalculation or change of circumstances.” Read more about it here.)

Correlating with the slight increase in Sanders’s support is a slight decrease in the number of voters self-identifying as undecided and an even slighter decrease in the number of voters expressing support for Clinton. Both of these decreases are only about 1% overall since January, although Sanders appears to have picked up the voters who supported former Democratic presidential candidate and Governor of Maryland Martin O’Malley. These voters temporarily spiked the undecided tally in the March version of this poll.

As of the latest installment in the survey, which was actually conducted last weekend, about 12% of Pennsylvania voters identify as undecided. That number was 13% back in January.

It is worth noting that most undecided voters who identify as such close to the election day itself often keep the independence of their decision as long as possible, in some cases taking their deliberations all the way to the voting booth. Senator Sanders has a history of doing well with these late deciding voters — when they are in demographics that are generally favorable to him, bringing the discussion to another issue for Sanders: favorability.

In the poll here discussed, Sanders’s approval rating was actually lower than that held by Clinton. Sanders had 33% of respondents express a “very favorable” feeling towards him, compared to Clinton’s 47%. Now, those numbers are nothing insurmountable, but still — approval ratings, as have been discussed on a national scale, are a strong indicator of a candidate’s ability to win an election.

Sanders has historically done a good job of overcoming hurdles like that, however, contingent on his ability to get his message out. On a national level, his approval rating only goes up along with awareness of who he actually is. That tradition works in Sanders’s favor in Pennsylvania, where he has weeks to get his name out, a short time, but the candidates know all too well that everything can change in a few weeks time.

As for the mobilization machine itself, Sanders has quite the ability to do just that. Tuesday night’s victory in Wisconsin for the Senator will give another huge boost to his campaign, which has out-raised the Clinton campaign 3 months in a row as of March.

So, just like across the rest of the nation, Pennsylvania is, in a way, a do-or-die for the Sanders campaign. He is gaining ground, though — expect a lot of action in the poll numbers in the last 3 days before the election, as has now happened across the nation as the various presidential campaigns trek on state by state.

Featured Image via Flickr, available under a Creative Commons license.