(CNN) The looming defeat of the Senate health care bill marks a dramatic low point in the otherwise lofty political career of Mitch McConnell, the chamber's majority leader who is often described as a disciplined "master tactician" of the Senate accustomed to methodically building legislative victories for Republicans.

But repealing and replacing the Affordable Care Act -- the hot button and emotionally-charged issue that sharply split his party -- proved to be too difficult a task for now, something McConnell acknowledged at a crowded Capitol news conference where he was asked bluntly if his "leadership" had been "damaged" by the process.

"This has been a very, very challenging experience for all of us," McConnell replied. "A lot of people have been involved in the discussion and very passionate discussions. But everybody's given it their best shot. And as of today, we just simply do not have 50 senators who can agree on what ought to replace the existing law."

It was a stunning admission for the GOP leader who made getting rid of Obamacare a mission since it was enacted seven years ago, and his top legislative priority for the past six months as Republicans controlled the White House and both chambers of Congress.

Few people in Washington bet against McConnell, who successfully negotiated highly complex deals in the past like the 2011 fiscal cliff agreement during the administration of President Barack Obama. The 75-year-old, soft-spoken Kentuckian, who has led Republicans for the last 10 years, also had the political fortitude to block Obama when he tried to fill a Supreme Court vacancy and successfully kept it open for a year until it was filled by President Donald Trump

"Mitch McConnell knows how to do things, and I think we're going to have some really great health care for a long time," Trump said at a Rose Garden celebration after the House passed its version of the Obamacare repeal and sent it to the Senate.

But McConnell drew immediate fire from some members of his Republican conference for his decision to bypass the "regular order" for health care, a process he so often advocates. Through that approach, committees of jurisdiction would hold public hearings and draft compromise legislation that could then move to the floor with significant support and momentum.

"The Congress must now return to regular order, hold hearings, receive input from members of both parties, and heed the recommendations of our nation's governors so that we can produce a bill that finally provides Americans with access to quality and affordable health care," said Sen. John McCain in a statement Tuesday from Arizona, where he is recovering from surgery.

Instead, McConnell created a small "working group" of about a dozen members, who happened to all be men , and huddled with leadership aides behind closed doors in his suite to try to cut a deal. Some Republicans were angered at being excluded and for the secrecy of the group.

JUST WATCHED McConnell: We can't agree on replacement Replay More Videos ... MUST WATCH McConnell: We can't agree on replacement 00:57

The group invited in other members -- like the handful of moderate Republicans from swing states concerned about potential cuts to Medicaid -- but somehow the force of those wary moderates' convictions didn't resonate fully with McConnell who thought that in the end, their espoused disdain of Obamacare would secure their votes no matter what.

In the end, it was that group of moderates that formed the bulwark against the bill, forcing McConnell to pull it from consideration before the July 4 recess and now to consider putting a revised bill on the floor where it appears destined for defeat.

"I did not come to Washington to hurt people," said Sen. Shelley Moore Capito, a West Virginia Republican, in a remarkable statement announcing her opposition to McConnell's latest proposal. "My position on this issue is driven by its impact on West Virginians. With that in mind, I cannot vote to repeal Obamacare without a replacement plan that addresses my concerns and the needs of West Virginians."

Conservatives also chaffed at the deal. Sen. Rand Paul, the other Republican senator from Kentucky, never got on board, claiming McConnell's approach never fully undid Obamacare.

McConnell also suffered by not having a consistent partner in Trump. The President never fully engaged in the negotiations nor in selling the deal. He didn't barnstorm the country selling the deal or hold many White House meetings to press wavering senators to get on board. Trump has invited all 52 GOP senators to 1600 Pennsylvania Avenue for lunch on Wednesday, a White Official told CNN.

Senate Republicans also did little to promote their efforts. They organized few of the typical press events on the Hill where advocates talk about the need for reform and McConnell rarely did TV interviews and other events to promote the bill. A CNN whip list of GOP senators show 41 of 52 not publicly supporting the bill.

Senate Republicans held a spirited closed-door caucus meeting in the Capitol at lunchtime. It was evident that senators were "upset," according to one GOP source briefed on the meeting. But the anger "was not all directed at" McConnell for his handling of the bill in part because "there are so many different factions" in the conference on the healthcare issue, the source said.

However, one conservative, Sen. Ron Johnson, R-Wisconsin, was furious with McConnell over reports the leader had said privately the long-term Medicaid reforms in the revised bill would never come to fruition, something McConnell denied.

Johnson was asked by CNN Tuesday if he still had faith in McConnell as GOP leader and he would not answer yes.

"I found those comments very troubling," was all Johnson would say.

Johnson appeared to be the only GOP senator so vocally upset with McConnell for his mishandling of the health care bill.

As McConnell moves now to have final votes on the bill sometime early next week, he must decide whether to return to "regular order" and try again to build support to reverse Obamacare or let the issue go for now and turn to other pressing business, like tax reform, government spending, an increase in the debt ceiling and other legislation.

Asked how he will explain to voters the defeat of health care after such a long commitment to passing it, McConnell was hopeful.

"Well, we have a new Supreme Court justice," he said. "We have 14 repeals of regulations. And we're only six months into it. Last time I looked, Congress goes on for two years."