(CNN) -- The happiest day in Justin Smith's life -- next to the day his daughter was born -- was March 5, 2013.
When his phone rang, he looked down and saw the 301 area code. It must be the National Institutes of Health, he thought. He didn't know anyone else in Maryland.
Indeed, Dr. Brigitte Widemann was calling to say that after five months of waiting, Smith's 12-year-old daughter McKenna had been accepted into a clinical trial at NIH headquarters in Bethesda, Maryland. She could begin the week of September 30.
Smith thanked the doctor and hung up the phone.
"Baby, hopefully we can get you a cure now," he said as he hugged and kissed his daughter.
McKenna has neurofibromatosis, a rare genetic disorder. Countless tumors in various parts of her body tangle around her nerves and grow into her soft tissue. One tumor the size of a grapefruit crushed her esophagus and her carotid artery when she was 4 years old. Another tumor collapsed a lobe of her right lung.
The growths are starting to cut off sensation to her right arm and left leg; soon she will lose function of them entirely. She's on four different pain medications, including two types of morphine.
McKenna has had two surgeries and 24 rounds of radiation. The tumors have continued to grow. She underwent medical experiments to use the drugs thalidomide and Gleevac. Both were a failure.
Doctors have told Smith his daughter will likely die before her 20th birthday. She turns 13 today.
"This NIH trial is her last hope," Smith said.
The Smiths boarded a plane Monday from their home in Cape Coral, Florida, to head to Bethesda. But during the trip -- even as they checked in at the Children's Inn at NIH -- they weren't feeling hopeful that McKenna would be able to start taking the experimental drug, called hydrogen sulfate, on Friday as scheduled.
Hydrogen sulfate, or AZD6244, has been tested in adults and children with cancer. NIH doctors think it might be able to prevent benign tumors like McKenna's from growing, or at least shrink the tumors and slow down their growth.
Smith feared the government shutdown would keep McKenna from being able to start the study at all.
McKenna is one of about 200 new patients, including some 30 children, who come every week to the NIH Clinical Center in Bethesda, Maryland, to begin clinical trials. These patients are being told they will have to wait until the government starts up again to start their trials, according to NIH spokesman John Burklow.
Taking care of McKenna, as well as her disabled grandmother, is a full-time job for Smith, a single father. An Army veteran, he's used to hard work and trying times, but as he waited Monday, Tuesday and Wednesday for word from the doctors, he grew more and more worried -- and angry.
On Wednesday he tweeted, "#governmentshutdown needs 2 end #Now hurting sick people. have the #House come here to apologize to my young daughter & others."
"Finally we're here and our government can't get its act together," he told CNN.
Then at 3 p.m. Wednesday, there was a turnaround. For reasons that are unclear, McKenna's doctors said she would be able to start taking the hydrogen sulfate on Friday as scheduled. No one knows how many other new patients like McKenna also managed to get into their NIH studies despite the government shutdown.
"If a child or adult patient is in desperate need for treatment, those people will be handled in a different manner," Burklow said, "and will more than likely be seen by physicians or nurses at the NIH Clinical Center."
While relieved that his daughter can start the trial, Smith worries about the kids who won't be able to. There are the other patients, like McKenna, who were supposed to start this week at the NIH Clinical Center, and if the shutdown continues, another 200 patients every week will face the same dilemma.
Even though McKenna's been lucky, the shutdown has still made her trip more difficult. With 75% of NIH's employees on furlough, the testing takes much longer than it should. An eye doctor's appointment this week, for example, should have taken one hour, but lasted more than three.
Exhausted and in pain, McKenna had to take a dose of morphine to get through it.
And then another setback, this one unrelated to the shutdown: doctors found a new tumor in McKenna's eye. This medical complication means she might not be able to get the drug Friday as planned.
Smith said he knows what he would do if he could talk to members of Congress in person.
"I'd put my daughter in their face and I'd say, 'Why are you putting politics above my daughter's life, or any other child's life?'" he said. "This is not a game."
McKenna said her message to Congress would be much shorter.
"This is stupid."
CNN's John Bonifield and Val Willingham contributed to this piece.