Absolutely.
If the president is still at 43-45% two years from now and Republicans nominate a decent candidate, Hillary Clinton will lose. It's not her at that point, it's just the president being unpopular. It's happened in the past and there's little to say Hillary Clinton has somehow broken the relationship between a president's approval rating and election day result.
W was far below low 40s. I think Truman was too. LBJ may have been close to that but that would be one case and a rare one with 3 different candidates winning states. A straight D vs R race with Obama in the low 40s wouldn't have much precedent.
See Reaganfan's answer for a bit of context.
My take on this is that essentially, the midterm cycles and last couple of Presidential election cycles have followed a pretty constant set of iron laws in American politics. (1) Voters tend to disapprove of the incumbent party in the midterms (2) Presidential elections are based on the incumbent's approval rating.
I believe that the party labels don't matter. I don't see anything "without precedent" - in fact, this upcoming election would be similar to 1952, 1968, and 2008. The incumbent president will almost certainly drag down the succeeding incumbent party candidate because of his unpopularity, and cap her ceiling. I also see little in the literature to suggest that succeeding party candidates can exceed the incumbent's re-election majority. That leads to another constant in American politics (3) Voters get tired of the incumbent party holding the White House and vote for "change" on a regular basis.
Unlike other precedents, they are pretty logical. A winning party usually has blowback because voters now hold them responsible for the nation's ills or voters supporting the losing party turn out in greater droves. Incumbent parties tend to wear out their welcome mats after years in office (the big reason only one Vice President has succeeded an incumbent President on his own in office since 1836).
Republicans learned this to our misfortune in 2008. I think seeing it play out on the Democratic side doesn't change that this is going to be a very difficult lift for the Democratic Party. Going off the 2008 example, John McCain did lead or was tied right after the Republican Convention and before the crash but would have probably lost narrowly to the President.
I've listed the falloff in the popular vote totals of incumbent parties vis a vis their successors. I'm trying to understand why Hillary Clinton would be any different.
However, the US presidential election isn't between a generic R and generic D. It is between two actual candidates. Granted, the inherent disadvantage for generic D means that Hillary Clinton is probably the only democratic candidate that could beat a reasonably strong GOP candidate (i.e. not Cruz, Palin, etc.). But she definitely could given her 100% name recognition, universal respect (even if some despise her) and longing back to the Clinton years. Well first off, I don't think Hillary Clinton is the best messenger. But it's like how we said in 2008, McCain could challenge the fundamentals of the election and defy Bush's poor approval rating. But even before the crash, Obama led McCain pretty consistently throughout the election year.
http://www.realclearpolitics.com/epolls/2008/president/us/general_election_mccain_vs_obama-225.htmlIt's pretty clear that an unpopular president, no matter what, will weigh you down, while a popular president can provide some cushion, if the economy's going well, for a same party candidate hoping to follow that president into office.
People don't vote based on nostalgia. They vote based on their approval of the incumbent, the economy's state on their personal lives, and whether the world's at peace or not. Democrats are pretty much trying to apply the McCain argument Republicans made eight years ago to Clinton's chances, and I think like the Republicans did eight years ago, it essentially hopes the fundamentals can be wished away.
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