After making major concessions on long-held ‘fiscal cliff’ positions, President Barack Obama and House of Representatives Speaker John Boehner will test the reaction of their respective parties in the US Congress and continue talks aimed at further narrowing their differences.

The effort is designed to avert the steep tax hikes and across-the-board spending cuts set to take effect unless a deal is enacted into law before December 31. Enactment would require a buy-in by the full US Senate and House on whatever Obama and Boehner present to them. Neither Obama nor Boehner can be certain yet on how much resistance they might meet.

Though much work remains, the progress contrasted dramatically with previous movement so slow that as recently as Sunday, some Washington insiders saw a 50-50 chance of going over the cliff – which the Congressional Budget Office says would bring on a new recession.

In rapid developments, the two sides came significantly closer to bridging gaps on critical issues such as tax hikes for the wealthy and cuts in social security cost-of-living benefits.

Obama and Boehner made the most headway on extending the reduced tax rates originally enacted in the Administration of President George W. Bush.

Both have agreed to keep the low rates for everyone but the wealthy, but they still differ on who qualifies as wealthy for tax purposes.

Obama, whose definition has for months been taxpayers above the $250,000 threshold, travelled to $400,000 in his latest offer. Boehner was at $1 million, but could move down to $500,000.