WASHINGTON — Sen. Patrick Toomey offered a simple, remarkable explanation this week for why Republicans have struggled so mightily to find a way to repeal the Affordable Care Act.

“Look, I didn’t expect Donald Trump to win, I think most of my colleagues didn’t, so we didn’t expect to be in this situation,” the Pennsylvania Republican said Wednesday night during a meeting with voters hosted by four ABC affiliates across his state.

Toomey, now playing a critical role in negotiations over the Republican health bill, spent most of last year criticizing Trump’s personal behavior and the fights he picked on social media. Toomey did not announce his support for Trump’s candidacy until polls closed in Pennsylvania last Nov. 8, fully aware that no Republican presidential candidate had won his state since 1988 – and assuming that Trump would continue the streak.

Toomey did not participate in detailed Republican planning sessions on the Senate Finance Committee about how to reshape the nation’s health laws if Trump won the election – because no such planning sessions were really ever held.

Every important Republican leader expected Democrat Hillary Clinton to win, and that left Republicans confused and paralyzed about how to proceed when she didn’t.

That in turn led to a rushed initial decision, made in consultation with House Speaker Paul Ryan, R-Wis., and Senate Majority Leader Mitch McConnell, R-Ky., during the presidential transition, to push for a full repeal of the 2010 health law and then set up a two- to three-year window in which Republicans would pass bills to replace it.

We all know how that has gone so far: The proposal was jettisoned amid a rank-and-file rebellion – and Trump’s own conflicting statements about what Congress should do. At one point, Republicans could not even agree on what metaphor to use to describe the process for replacing the law. Ryan referred to “buckets,” while others called for “rescue missions” and some talked about “backpacks.”

That the Republicans didn’t believe they would take back the White House has informed other policy debates this year. A massive overhaul of the tax code, a Holy Grail of policy for Ryan, remains completely at loggerheads because the speaker’s preference for a controversial tax on imported goods was never litigated within the party last year, ahead of the election.

Similarly, Trump’s call for a $1 trillion infrastructure plan is still sitting in neutral because congressional Republicans, long averse to big spending projects, never embraced it nor even turned their attention its way.

Perhaps nowhere did the surprise factor of Trump’s victory show its impact more than in the effort to fill top jobs inside the administration. Clinton’s campaign, fully expecting victory, was stocked with hundreds of volunteer advisers who were already angling for sub-Cabinet-level posts in key agencies including the departments of State, Justice and Defense. Many of them were current or former senior staff to congressional Democrats.

But with Republicans, those connections were rare because few believed them to be worth the effort. No more than a handful of senior Republican aides from Capitol Hill boasted connections to the Trump transition team. And only in recent weeks have some of the smartest and most influential advisers to Senate Republicans been nominated to key positions at Treasury and State.

Trump’s struggles on Capitol Hill reflect more than institutional shock over his victory. Republicans have controlled the House and Senate for more than five years, with little success working out these policy issues.

And Trump’s advisers have not always lent a helping hand in the six months since he was inaugurated. Aides have regularly gone to war over key policy objectives and left Hill Republicans guessing which way the wind was blowing inside the West Wing. Early this year, Stephen Bannon, Trump’s chief strategist, praised Ryan’s border tax proposal as “a first step of economic nationalism,” yet while a few weeks later Treasury Secretary Steven Mnuchin told House conservatives that Trump opposed the plan.

And Trump’s own public musings, sometimes in media interviews and sometimes on Twitter, have also sowed division on policy matters – and scared away top Republican talent from senior administration posts.

But the shock of his victory, and the lack of planning ahead of it, is perhaps the cornerstone of this summer of Republican gridlock.

In December 2015, Republican lawmakers vote easily to repeal the Affordable Care Act. But it was a “messaging” vote, and they knew that then-President Barack Obama would veto the bill. Now, as Toomey likes to say, they’re playing with “live ammo.”

Eight months after Trump’s stunning victory, Republicans are still coming to grips with what they can actually pass and sign into law even with full ownership of all the levers of power.

“Given how difficult it is to get to a consensus, it was hard to force that until there was a need to,” Toomey said Wednesday.

Eight years ago, Democrats had been planning for months for the possibility of full control of Congress and the White House. Leading up to the 2008 elections, the chairmen of the finance and health committees, Max Baucus and Edward M. Kennedy, held meetings with key health-care industry stakeholders about early thoughts on what would become the Affordable Care Act.

Many policy disputes still had to be litigated throughout 2009 and early 2010, but congressional Democrats and Obama laid out from the outset the process they would pursue to pass the legislation.

Republicans have not had that luxury. They have themselves to blame for not being ready from the outset to handle the health-care issue and others. Now, we know they admit it.

Said Toomey at his town hall on Wednesday: “I think that’s a valid criticism.”