Without waiting for results from elections on Tuesday that few in the White House expect to go well for Mr. Obama, top aides have met for weeks to plot the final quarter of his presidency. Anticipating a less friendly Congress, they are mapping possible compromises with Republicans to expand trade, overhaul taxes and build roads and bridges.

For a president who has lost public support and largely failed to move his agenda on Capitol Hill since winning re-election two years ago, there may be little hope for significant progress if Republicans capture the Senate and add to their House majority. But if Republicans are fully in charge of Congress rather than mainly an opposition party, both sides may have an incentive to strike deals, at least during a short window before the 2016 presidential campaign consumes Washington…

Among advisers inside and outside the White House, there is a growing sense that Mr. Obama has closed himself off within a shrinking circle of aides. Some advisers who had been influential said they were no longer consulted as much. They worry that Denis McDonough, the White House chief of staff, has taken on too much himself.

“The circle is small,” said a former senior administration official who did not want to be identified discussing former colleagues. “Particularly if the Republicans take over, I would like him to expand that group and bring in some people from the outside.”