Ted Kennedy, the renowned Democratic senator, fell ill with brain cancer in the middle of the 2008 presidential campaign. His diagnosis shaped the emotional backdrop for the debate that began a few months later over his signature issue, national health care.
When he died the following year, his decadeslong passion became a rallying cry for fellow Democrats. President Barack Obama signed the Affordable Care Act into law a few months later.
Kennedy's friend Sen. John McCain has now fallen ill with the same disease. Because of his transcendent reputation for courage and patriotism, news of McCain's illness shocked Washington with rare force. Could McCain's battle have a similarly galvanizing effect on major debates rattling the Capitol now?
One immediate effect is obvious. Senate GOP Leader Mitch McConnell has such a small margin for error that McCain's medical absence could be the difference between success or failure in the Senate even taking up its Obamacare repeal plan next week. Depending on how long he is sidelined, it could have a similar effect on deliberations over the budget and tax reform.
But McCain promised over Twitter on Thursday that he would return to Washington soon.
Any broader, emotional effect would depend on how he chooses to direct his energies. The unique circumstances of the 2017 landscape offer reasons to doubt that McCain's illness will create momentum for any particular change. For one thing, the foremost legislative debate right now has not been a dominant thread of McCain's career.
He has not wholeheartedly embraced either expansion of the federal role in health care or repeal of Obamacare. In the Senate debate thus far, he has grumbled about the process without signaling he would stand in the way.
Still, McCain has the potential for a larger impact on how other Republicans resolve their growing concerns about President Donald Trump. He has long made clear his concerns about the New York billionaire who once questioned his Vietnam heroism, calling the scandal over Russia's interference in the 2016 election "a centipede" from which investigative shoes would continue to drop.
For the moment, Justice Department special counsel Robert Mueller has more influence than anyone over how GOP lawmakers handle Trump. Until the ex-FBI director completes his investigation and announces conclusions, Mueller offers them a political shield.
"As long as the policy agenda lives, [Congress] will defer Russia stuff to Mueller and not offer much beyond furrowed brows and frustrated sound bites about unfortunate distractions," said GOP strategist Liam Donovan.
Still, the signature of McCain's career has been elevating country over party. Should his party's 2008 presidential nominee decide to make confronting Trump a test of Republican patriotism, he could turn up the heat on both the president and his fellow colleagues.