WASHINGTON — Three days after an extraordinary forum moderated by President Obama to bridge the gulf between Democrats and Republicans over a health care, leaders of both parties drew clearer lines in the sand on Sunday.

As they did so, the months-long confrontation over health care seemed to lurch closer to the use by Democrats of a controversial parliamentary maneuver for passage.

President Obama spent hours on Thursday with Republicans and Democrats at a session aimed at finding common ground. But the Republican Senate leader, Mitch McConnell, said Sunday that there was probably no way Mr. Obama could win a single Republican vote, even if he were to remake his health-care plan.

And another senior Republican, Senator Lamar Alexander of Tennessee, warned that Democratic use of the maneuver known as reconciliation, requiring 51 votes for Senate passage, would amount to “political kamikaze,” exploding in the Democrats’ faces in the November mid-term elections.