President Barack Obama is aggressively pushing an ambitious agenda to liberalise global trading.

But already political trade wars are forming, and they're with fellow Democrats rather than with Republicans, his usual antagonists.

Obama is promoting free-trade proposals with Europe and Asia that could affect up to two-thirds of all global trade.

The ambitious deals would reduce or eliminate tariffs and other trade barriers. But there's trouble ahead for both the Trans-Pacific Partnership and the Trans-Atlantic Trade and Investment Partnership - at the negotiating table and from Congress.

The deal with Europe will be a top item this coming week in Northern Ireland at the Group of Eight summit of major industrial democracies.

The Asia pact was brought up pointedly by the new Chinese president, Xi Jinping, in his California meetings with Obama last weekend.

Republicans historically have supported free-trade agreements far more than have Democrats, and a politically weakened Obama may not have enough second-term clout to successfully twist the arms of enough Democratic lawmakers.

Some Republicans who usually vote for easing trade barriers may vote "no" just because the agreements will bear Obama's signature.

Both deals generally have the support of US businesses. But labour unions and human rights and environmental groups - core Democratic constituencies - have so far viewed them cynically.

These organisations, and Democrats in general, say that free-trade deals can cost American jobs and lead to environmental and workplace abuses that would not be tolerated in the US.

"We certainly have concerns," said Celeste Drake, a trade and policy specialist at the AFL-CIO, the nation's largest labour federation.

Obama worked to overcome Democratic resistance to win passage in 2011 of trade pacts with South Korea, Panama and Colombia, completing negotiations begun by his Republican predecessor, President George W Bush.

The talks for a new Asia-Pacific free-trade zone came up in the Obama-Xi meetings last weekend. - Reuters