Raising the debt ceiling is something that everyone agrees must happen. Congress must pay the bills for the spending that Congress has ordered. This is not a concession. John Boehner wants to raise the debt ceiling, Mitch McConnell wants to raise the debt ceiling, Barack Obama wants to raise the debt ceiling. Everyone agrees. There is nothing to negotiate about.
1) Republican leaders will ultimately agree to raise the debt ceiling, and they know it, because they themselves have previously admitted that not doing so will badly damage the economy.
2) Because of the above, a hike in the debt ceiling is not something that Democratic leaders want and that Republican leaders don’t. In other words, it is not a typical bargaining chip in negotiations, in the way spending cuts (which Republicans want and Dems don’t) or tax hikes (which Dems want and Republicans don’t) are.
3) And so, if and when Republicans do agree to raise the debt ceiling, it will not constitute any kind of concession on their part — even though they will continue to portray it as such to demand concessions in return. It will only constitute Republicans agreeing not to damage the whole country, which does not constitute (one hopes) them making a sacrifice.