Apparently there is no limit. Read this editorial in the New Republic:
That's what makes the road to the Denver convention so damn frustrating. John McCain is heir to a presidency whose accomplishments now include an economy careening toward a deep recession; on issue after issue, public opinion mirrors the Democrats' policies. This should be the one election that even the party of Dukakis couldn't screw up.
First of all, we are not certain that there will be a recession. There might be, but if so there is no reason to believe that it will be deep. It may be very brief and mild like the last two recessions. This is wishful thinking on the part of Democrats. They want a recession so they can blame it on Bush. Just like they blamed the 2000/2001 recession on Bush, even though it began during Clinton's last year.
Furthermore, even if there is a deep recession, the lefties might not be able to successfully blame it on Bush. The Democrats control both houses of Congress, and the voters might give some or all of the blame to them. And even if the Democrats and their perpetual allies in the media are able to give Bush the blame, it might not transfer to McCain. He and Bush have often been at odds in the past.
"on issue after issue, public opinion mirrors the Democrats' policies". I know of at least one position that public opinion does not mirror the Democrats' policies. The authors of the editorial address this issue:
Where it once looked like Bill Clinton and Al Gore had helped purge the party of the lame identity politics that had ruined Democratic candidates for a generation, discussions of race and gender have returned with a vengeance. Supporters of Clinton and Obama compete to prove who is the bigger victim--opponents are casually tarred as sexist or racist.
This issue was never 'purged' by Clinton or Gore. It was only swept under the rug. Democrats favor racial preferences for ethnic minorities. And anyone who opposes them is casually tarred as sexist or racist. It is no wonder then, that the Democrats have not carried the majority of the popular vote in a presidential election since 1976. Nor have they carried a majority of the white vote since 1964.
In the current campaign, neither candidate has come close to approaching his [Bill Clinton's] level of clarity, especially when it comes to the issue that offers Democrats the simplest path to the presidency: the economy. They have failed to articulate a critique of the wild Bush-era deregulation that has allowed the greed of banks to run amok.
There have been no significant acts of financial industry deregulation during Bush Jr's administration. Riegle-Neal, which allowed interstate banking, and Gramm-Leach-Bliley, which allowed commercial banks to engage in investment banking, and vice-versa, were both passed during the Clinton administration.