what domestic issues?

I can't speak for everyone, but Dean's main appeal to me is his stance on domestic policy. However, as Iraq war fever builds to a pitch, it's unsurprising that Dean's message on the campaign trail is being driven/pulled by foreign policy issues, and foreign policy has dominated all his recent media appearances (which has put him in danger of being marginalized in conventional wisdom as the anti-war candidate).

Given that Dean has no foreign policy experience, only opinions, this has made him vulnerable in certain ways. For example, regarding the Israel-Palestine conflict, Dean is already considered a potential "hawk in dove's clothing" :

In his major foreign policy address to date, a February 17 speech at Drake University in Iowa, Dean blasted the Bush administration’s foreign policy regarding Iraq and several other areas, but – when it came to Israel and Palestine – the former Vermont governor declared that, while the United States should become more engaged, he did not have any fundamental objections with President George W. Bush’s policies. Dean called for an end to Palestinian violence against Israeli civilians, but he did not call for a cessation of Israeli violence against Palestinian civilians. Similarly, there was no call for an end of the Israeli occupation, for Israeli compliance with UN Security Council resolutions, or a withdrawal from Israel’s illegal settlements in the occupied territories or even a freeze on the construction of new settlements.
...
Dean also appears to reject the widespread consensus among Israeli peace activists and Middle East scholars that Palestinian terrorism is a direct outgrowth of the 35-year Israeli military occupation. Instead, Dean seems to argue that terrorism itself is the core issue. He also rejects calls by APN and other liberal Zionist groups that Israel’s requested $12 billion loan guarantee be linked to an Israeli freeze on constructing additional illegal settlements on confiscated Palestinian land, arguing that such aid should instead be unconditional. Pushing for such a dramatic and unconditional increase in financial support for the incumbent government just before Israelis went to the polls in January was widely seen as a not-too-subtle endorsement of Sharon’s re-election.
...
There are indications, however, that Dean’s position on Israel and Palestine is not firm. Aides of the candidate claim that the former governor – who has focused on domestic issues up to this point in his political career – is still in the process of developing his position on this and other foreign policy concerns and could still be swayed to take a more moderate stance. Whether or not he will hold on to his initial hard line position will depend in large part on whether peace and human rights activists will embrace him despite his apparent hawkish views or reject him as being too similar to Bush and the Republicans.

Whatever your opinion on Israel-Palestine, you can appreciate the gulfs that Dean will hae to bridge to be acceptable as a progressive candidate that liberals and progressives can unify behind. But Dean's critiques come from the right as well as the left (within the context of liberal-progressives). An essay in the New York Observer mentions that Kerry is already spinning Dean as beholden to the UN:

On Iraq, Kerry campaign manager Jim Jordan told the Associated Press that Mr. Dean wanted to give the U.N. "veto power over national-security decisions," and that it was "an extraordinary proposition, one never endorsed by any U.S. President or serious candidate for the Presidency."

Joe Rospars, who brought the NY observer piece to my attention, has a defense of Dean against the UN-lackey charge.

Overall, Dean will continue to be exposed from both the left and the right. A moderate is easy pickings on foreign policy, the inverse of domestic issues where moderates are king. Dean needs to resist attempts by the media to probe foreign policy issues, by responding clearly with his positions, and steering the debate back towards domestic affairs.