The prospects for an election-year Senate bill aimed at beefing up benefits for America's veterans are caught in the dispute over whether to impose sanctions on Iran.

Democrats resumed trying to push legislation through the Senate on Wednesday that would allow more veterans get treatment at Department of Veterans Affairs facilities, expand dental care and fertility treatment and bolster education and job-training benefits.

Helping veterans is popular with both parties. But Republicans are demanding a vote on an amendment that would reduce the costs of the $21 billion legislation — and also impose fresh sanctions on Iran if ongoing negotiations over curbing that country's nuclear program fail.

President Barack Obama opposes those sanctions, saying international talks should be given a chance to succeed. Senate Majority Leader Harry Reid, D-Nev., has blocked attempts to hold a vote on the sanctions — which mirrors earlier bipartisan legislation that garnered 59 co-sponsors and had the potential to pass the chamber and embarrass Obama.

If Reid denies Republicans a vote on the amendments, GOP senators may use procedural moves to block the veterans measure from reaching final passage.

Harsh words from both sides Wednesday made that outcome seem increasingly likely — a day after senators voted 99-0 to allow debate on the legislation to begin.

Reid said the GOP push to include Iran sanctions in the veterans bill was "obstruction at its best" and added, "Republicans obviously have no intent of doing anything for the veterans."

Senate Veterans Affairs Committee Chairman Bernie Sanders, I-Vt., said it would be "extremely disrespectful" to veterans to use the legislation "as nothing more than a political pawn for other issues."

Senate Minority Leader Mitch McConnell, R-Ky., said attaching the Iran sanctions to the veterans bill would enhance the prospects for sanctions and added, "There is no excuse for muzzling the Congress on an issue of this importance to our own national security" and the security of other countries.

"If he doesn't allow Republican amendments, I think the path forward is probably going to kill the bill," Sen. Richard Burr of North Carolina, top Republican on the Veterans committee, said of Reid.

The two parties have been battling for months over amending Senate legislation. Democrats say Republicans are only interested in forcing politically embarrassing votes, while Republicans say Democrats are autocratically shutting down the chamber's amendment process.