Loose ends in probe give Trump a lifeline.

None of the witnesses could directly link the US president to the Ukrainian scandal. After two weeks of riveting public hearings in the House impeachment inquiry into US President Donald Trump, there is a mountain of evidence that is now beyond dispute. Trump explicitly ordered US government officials to work with his personal attorney Rudy Giuliani on matters related to Ukraine, a country deeply dependent on Washington's help to fend off Russian aggression.

The Republican president pushed Ukraine to launch investigations into political rivals, leaning on a discredited conspiracy theory his own advisers disputed. And both American and Ukrainian officials feared that Trump froze a much-needed package of military aid until Kyiv announced it was launching those probes. Those facts were confirmed by a dozen witnesses, mostly staid career government officials who served both Democratic and Republican administrations. They relied on emails, text messages and contemporaneous notes to back up their recollections from the past year. Stitched together, their hours of televised testimony paint a portrait of an American president willing to leverage his powerful office to push a foreign government for personal political help.

That alone has many Democrats on the brink of voting to impeach Trump before the end of the year, potentially pushing toward a trial in the Senate. Yet the witness accounts left one prominent hole that offered a lifeline for Trump and his GOP allies. None of the witnesses could personally attest that Trump directly conditioned the release of the $400 million in military aid on a Ukrainian announcement of investigations into former Vice-President Joe Biden and the Democratic National Committee. Some Republicans suggested that even if that link could be made, it wouldn't be enough for them to support impeaching Trump and removing him from office. And without that link, Trump's wall of support among GOP lawmakers seems formidable.

"I have not heard evidence proving the president committed bribery or extortion, " said Rep. Will Hurd, a moderate Republican from Texas who is retiring from Congress next year and would be a bellwether for any signs of weakness in GOP support for the president. Like some other Republicans, he made clear he...