Republicans have had trouble mounting an effective defense on President Trump’s Ukraine call, because they haven’t put down their stakes on the most defensible ground.

Complaints about House Democrats’ less-than-transparent impeachment process, though justified, were clearly perishable once Democrats adopted more regular proceedings.

The contention that Trump’s phone call to the Ukrainian president was “perfect” was never going to withstand scrutiny. The line that there was “no quid pro quo” has become steadily less plausible as more testimony has emerged suggesting that Trump withheld security aid to Ukraine in the hopes that the Kiev government would announce an investigation into the 2016 election and the gas company Burisma and/or Joe and Hunter Biden.

The best defense Republicans can muster is that nothing came of it. An ally was discomfited and yanked around for a couple of months before, ultimately, getting its military aid.

All of this bears some resemblance to Trump’s alleged obstruction of justice during special counsel Robert Mueller’s investigation into “collusion.”

Trump hated the investigation and wanted it to go away, and even plotted against it, but at the end of the day, Mueller did his work. More specifically, the Ukraine mess is a lot like Trump’s order, or purported order, to then-White House counsel Don McGahn to fire Mueller. After drama, internal contention and tragicomedy, nothing happened.

One of the hallmarks of the Ukraine maneuverings last summer is confusion about what US policy was — and who was making it and how determined they were to get the Ukrainians to agree to investigations. This is a symptom of the back channel represented by Rudy Giuliani operating on a separate track from official channels, but also of a legitimate dispute about the US approach toward Ukraine until the very end, when the defense funding was released on Sept. 11.

According to US Ambassador to Ukraine William Taylor, security assistance didn’t come up in a meeting between then-national security adviser John Bolton and Ukrainian President Vlodymyr Zelensky on Aug. 27, two weeks before the funding was ­released.

When Vice President Mike Pence visited and met with Zelensky on Sept. 1, he didn’t mention the investigations.

In Taylor’s telling, as late as early September, Ukrainian officials were asking why the funding was being withheld, and their US counterparts couldn’t tell them.

Meanwhile, the hold was widely opposed within the US government. As Taylor put it, “at every meeting, the unanimous conclusion was that the security assistance should be resumed.” Indeed, officials at the center of Ukraine policy were scheming against the scheme to get Ukraine to commit to the investigations.

The rejoinder to all this is that the furtive and ambiguous ­nature of the interaction with the Ukrainians may well point to a cognizance of its impropriety.

True enough, but the offense here shouldn’t be exaggerated. It’s not as though Trump was asking the Ukrainians to frame anyone, or give him bags of cash, or buy advertisements in swing states. The sought-after announcement of an investigation into Burisma, a company with a demonstrably shady past, wouldn’t have constituted an ­investigation into Joe Biden, or even an investigation into Hunter.

Trump surely would have used such an announcement to argue that Hunter Biden is corrupt, but you might have noticed that Trump is arguing that Hunter Biden is corrupt, regardless.

Special envoy to Ukraine Kurt Volker has said he had a relatively relaxed attitude toward the hold on the funding. “I believed the decision would ultimately be reversed,” he said in his opening statement. “Everything from the force of law to the unanimous position of the House, Senate, Pentagon, State Department, and [National Security Council] staff argued for going forward, and I knew it would just be a matter of time.”

He was right. You might say it never should have gotten to that point. What you can’t say is that the money was ultimately kept from the Ukrainians — or that they opened an investigation of the Bidens.

Rich Lowry is the editor of ­National Review and author of the forthcoming book “The Case for Nationalism: How It Made Us Powerful, United, and Free.”