First, Jagdish Bhagwati, long a critic of preferential trade agreements and a proponent of unilateral free trade as well as the WTO’s multilateral process, suggests that the United States poses the most formidable barrier to further efforts to free trade, particularly in agriculture:

While the Doha negotiators have settled many important issues, the final negotiations first stalled last year, owing to America’s refusal to cut its agricultural subsidies further and India’s insistence on special safeguards to prevent exposing its millions of subsistence farmers to unfairly subsidized US competition.
Today, domestic politics in the US and India has left America as the only stumbling block to progress. The last election freed India’s Congress Party of its coalition with the Communists, who opposed trade, and thus increased the flexibility of pro-trade Prime Minister Manmohan Singh. But the last election in the US ushered in a Democratic congressional majority that is indebted to trade-fearing unions, thus constraining the pro-trade President Barack Obama.

This sounds like a fair assessment. Bhagwati offers a potential way forward:

The other option is to close the Round by resolving the US-India discord on agriculture. Mutual concessions can be crafted that ensure negligible political fallout for both leaders. This would also require marginal improvements in concessions by the major developing countries, and by the US and the European Union on services.
The problem is that lobbyists in Washington would reject this modest solution if the Doha Round were the end game.

One wonders if Bhagwati is being too optimistic.

Dan Griswold has an item at Cato on the wonderfully named miscellaneous tariff bill.