Americans are pretty evenly divided on whether they'd rather have four more years of Barack Obama or replace him with a Republican in 2012, with 48% going for Obama and 47% with a generic Republican. But with the exception of Mitt Romney none of the actual top tier Republican candidates poll as well against the President as the hypothetical one.
Obama leads Romney 47-46, matching his generic ballot lead. Obama's lead expands to 48-45 over Mike Huckabee, 49-43 over Newt Gingrich, 51-42 over Sarah Palin, and 48-37 over Marco Rubio who PPP followers voted in as this month's 'wild card' candidate.
Obama's not getting any more popular- as has been the case on every PPP national poll since the spring more voters disapprove than approve of the job he's doing. This month it's 47% approving and 50% disapproving. But they don't care for any of the leading Republicans either. Huckabee's favorability comes out best at a net -1 (39/40). He's followed by Romney at -6 (36/42), Palin at -17 (38/55), and Gingrich at -20 (33/53). The fact that every leading Presidential candidate is viewed dimly by the American public is pretty reflective of the continuing high level of dissatisfaction with politicians in the country.
Obama does the same with Democrats against all of the top 4 Republicans, getting 83-84%. There are big differences with Republicans though. Romney and Huckabee each get 87% of the GOP vote, but Gingrich gets only just 81% and Palin's even lower at 79%. There's a small but meaningful group of Republicans who are very hesitant to commit to supporting Gingrich or Palin even if they end up with the party nomination. There's also a wide divide with independents depending on whether the GOP nominee is Palin or one of the others. Obama ties Romney with them and leads Huckabee and Gingrich by only 2 and 3 points respectively with them, but against Palin his advantage expands to 12 points.
Bottom line- Obama is weak but for now the Republicans are even weaker. There's a long way to go.
Full results here