(CNN) The UK will return to the polls on Thursday for its second general election in a little more than two years, as the ruling Conservative Party seeks to strengthen its majority ahead of what are expected to be difficult negotiations to leave the European Union following 2016's Brexit vote.

That it's happening at all came as a surprise to even British politicos. Prime Minister Theresa May called for the vote only seven weeks ago, in mid-April, when her right-leaning Conservative Party was surging in the polls. But the narrative has taken an unexpected turn as decision day nears. The left-leaning Labour Party and its socialist standard-bearer, Jeremy Corbyn, are believed by some prognosticators to be narrowing the contest -- and could now stand an outside shot at toppling May's government.

With so much at stake, the progressive cavalry has turned up to aid Labour's efforts ahead of the vote. Claire Sandberg, an American activist and former digital organizing director for Bernie Sanders during his primary bid, is in the UK now, advising Labour-aligned groups working to defeat May and the Conservatives.

I spoke to Sandberg over email on Monday about what she's doing, the state of the race and how its results might affect the US political scene. Here is a transcript of our conversation, lightly condensed and edited.

Krieg: First, the news. There have now been two terror attacks during your time in the UK -- Manchester and then, of course, on Saturday night in London. So that's three in a relatively short period of time. Will the attacks weigh on voters -- and could they tilt the results on June 8?

Sandberg: There's no way for the attacks to not be on the minds of many voters. The sense that these attacks are rare or difficult to plan, or that after police raids and arrests people will be safe for a while, is giving way to the expectation that more attacks like these may be inevitable, and could come at any time.

But how that increased worry about terrorism will play out politically may not be in the way outsiders would expect.

The tabloid press was already in overdrive even before this latest attack, trying to paint Corbyn as soft on terrorism because of his talks with Sinn Fein , the Irish nationalist party, in the 1970s and 1980s. But I think, increasingly, many voters are seeing that line of argument as a cheap political attack that doesn't bear any relevance to today's terror threat, and they feel that Theresa May, who was home secretary for six years before becoming Prime Minister, has a lot more to explain to voters.

In particular, she's drawing a lot of criticism over her drastic cuts to the police forces -- there are 20,000 fewer officers now than there were in 2010. Law enforcement leaders had previously voiced alarm over those steep cuts, but May accused them of "crying wolf."

May's response to London Bridge has been to call for censorship on the Internet and a new agency to counter extremist ideology, but her four-point proposal was immediately blasted by former top law enforcement officers, who decried her cuts and said that May had only been able to temporarily step up the police presence following Manchester by forcing cops to work 16-hour days and take mandatory overtime. Now, May and her deputies are scrambling to explain themselves, while Jeremy Corbyn is calling for the cuts to be reversed and for security services to be fully funded.

So yes, the terror attacks will certainly be on voters' minds on Thursday, and this is an active situation; even as I write this to you I just got an alert about a former top aide to David Cameron, Steve Hilton, saying May was "responsible" for the London Bridge attack and should step down instead of seeking re-election.

Theresa May responsible for security failures of London Bridge, Manchester, Westminster Bridge. Should be resigning not seeking re-election pic.twitter.com/2o0odey2BQ — steve hilton (@SteveHiltonx) June 5, 2017

(Note: Later Monday, Corbyn echoed calls for May to resign as PM over the police cuts.)

Krieg: Let's talk basics. I think the shorthand in the US is that the UK Conservatives (or Tories) are like our Republicans and that Labour has most in common with the Democrats. Is that a good baseline of understanding?

Sandberg: The UK is still a multi-party parliamentary system, so the two biggest parties don't have the same near-total monopoly on public support that our two biggest parties in the US have. But that's still a good starting point.

Labour as a party has its roots in the trade union movement, and over most of the course of its history has fought for the rights of working people and for a strong public sector. And the Conservative Party has long been the party of big business and the very wealthy, and pushed to break the unions, privatize the public sector, and cut taxes for the rich. You don't have the same religious social conservatism that is so important to the US Republican coalition, but you do have a hard-right element.

Theresa May recently adopted many of the policies advocated by the UK Independence Party (UKIP), which has a strongly anti-immigrant and anti-Muslim agenda and was a driving force behind Brexit. She also controversially refused to join other European leaders in criticizing Trump's Muslim ban, and is rolling out a new plan for Internet censorship.

All of this begs the question of how US Democratic operatives like Jim Messina, President Obama's former campaign manager (in 2012), could work for a politician like May, who so clearly stands in opposition to basic liberal values of fairness, equality, free speech -- to say nothing of her agenda of extreme austerity and increased corporate power.

Theresa May strong, confident, shows she has a plan for a stronger Britain #bbcqt — Jim Messina (@Messina2012) June 2, 2017

Krieg: Which brings to mind another comparison you'll often hear in the US -- that Jeremy Corbyn, the Labour leader, is "the British Bernie Sanders." Or vice versa. You worked on the Sanders campaign in 2016. How accurate is that?

Sandberg: It's not hard to draw parallels between Bernie Sanders and Jeremy Corbyn.

They're both populists and outsiders who challenged the establishments of their own parties, energized new movements of people and in particular brought young people into politics, who are fighting to reverse the extreme wealth inequality and massive consolidation of corporate power that is ruining our societies.

Now, to be clear, I don't think they're identical in every regard, and there are some important differences between them. But they have both tapped into the desperation of a lot of people who -- after 30 years of neoliberal economics, attacks on unions, and cuts to the public sector -- have seen their real wages fall and their benefits cut. And both have tapped into the palpable fear of young people who are facing a bleak future defined by unending economic anxiety and extreme climate change.

Ultimately, the unexpected success of both Bernie and Corbyn demonstrates that a lot of people on both sides of the Atlantic are fed up with failed status quo politics, and are hungry for genuine solutions to the multiple intersecting crises we face as a society.

Krieg: Having worked on a US presidential campaign, is there anything about the UK process that's surprised you -- anything from an organizing perspective that you were surprised they do not typically try?

Sandberg: The biggest surprise to me was that campaigning in many places is very narrowly focused on turning out existing party members, or in some cases even just data collection.

In the US, that can be an issue as well, with campaigns that devote all their energy to turning out a very small segment of the electorate -- rather than expanding the base of support by registering new voters, or trying to persuade non-supporters. But it does feel more severe here, in large part because virtually all voter contact is run directly by the parties, which have standing bureaucracies that carry over from year to year.

So campaigning tends to be done in a certain, regimented way, and it's very difficult to try doing things differently. That's why it's been especially exciting to bring techniques like deep canvassing -- a research-backed voter contact method focused on listening and drawing out the person you're talking to -- to key marginal seats where it will be critical to expand the electorate and even convince voters to cross party lines.

Krieg: Over the last couple weeks, there have been reports -- some based on polls, others using narrower measures -- that Labour might outperform what had been really low expectations. You're there, do you see it?

Sandberg: There's no question that there's been a massive shift since the election began.

And I think, even if some of the polls turn out to have been overly favorable to Labour, Labour will still unquestionably have had a truly enormous turnaround. One big reason for the shift in the polls nationally has been a massive surge in young people, who overwhelmingly support Labour, saying they're going to turn out. But it's not just increased youth voter turnout. You've also seen huge drops in approval ratings for May and droves of voters abandoning the Conservatives.

Oxford #myvotecounts rally hears from @BernieSanders aide @clairesandberg how to barnstorm. Have conversations, knock on doors, get vote out pic.twitter.com/zMoRrASsEL — Louise (@LLocock) May 20, 2017

You can draw a direct line on all of these shifts back to the manifestos that the two major parties released. Theresa May's initial overture to voters was to ask people from all parties to "lend" her their votes to give her a stronger hand negotiating Brexit with the European Union. But the manifesto revealed that a Conservative government would actually mean forcing elderly people with Dementia to sell their homes to pay for their care -- the so-called "Dementia tax" -- and eliminating school lunches for 900,000 school children, among other things. And it has shown that a Labour government would mean protecting the National Health Service, stopping the deep cuts to social services, and eliminating university tuition fees.

Corbyn's manifesto delivers for people who are in the core Labour coalition, and gives people who might have been nervous about him -- after years of fear-mongering and red-baiting in the tabloid press -- a reason to believe that his ideas are in fact rather sensible.

May's manifesto , by contrast, is almost Dickensian in its cruelty. And in the wake of the catastrophic rollout of the Dementia tax idea in particular, May flip-flopped and withdrew the plan or, as they say here, "U-turned" on it, just four days after introducing it -- which is of course the opposite of the "strong and stable" leadership she promised when she began her campaign.

Krieg: How much of a say will the smaller parties -- Liberal Democrats, the Greens or UKIP, for example -- have in determining the shape of the next UK government?

Sandberg: A big factor that could impact the overall makeup of Parliament is a huge upsurge in tactical voting, and increased cooperation between the left parties in some critical swing areas. Again, while the UK has two dominant parties, it's still a multi-party system, and in contrast to the US where other parties are much more marginal and virtually only ever act as spoilers, in the UK many of those parties hold seats and have strong regional pockets of support.

While in 2015, the UK Independence Party took a significant number of votes away from the Conservatives, the left has been hurt much more by the lack of cooperation between parties than the right. This election people on the left are determined to not let that happen again. So voters in many places are setting aside deeply held allegiances to vote for the party best positioned to win, and in a handful of marginal seats, the parties themselves have either formally stood down or decided to not actively campaign and offer tacit support to a competing left party. In most but not all cases, this has meant voters from smaller parties throwing their support behind Labour.

"This manifesto is about what we have to do as a society. People want hope, people want change." - @labourlewis pic.twitter.com/fLfsgPO3BF — Claire Sandberg (@clairesandberg) June 3, 2017

This cooperation would be significant at any point, but it's especially striking with Corbyn as the leader of Labour, and it actually gives me some faith that we'll be able to get through our civil war within the Democratic party back in the US. Since last November, I've often wondered what would have happened if Bernie had been the Democratic nominee -- would Clinton supporters have rallied around him to stop Trump, or would their hatred of the left have overridden their desire to save the country from disaster? Would they have drafted (former New York City Mayor Michael) Bloomberg to run as an independent, or otherwise rooted for Bernie to fail?

At the point that the Conservatives called the election, they made the calculation that voters broadly and even people within Labour hated Corbyn so much that they wouldn't be able to unite, and so the Conservatives would win a landslide. At that time, some establishment Labour figures openly welcomed a massive Labour defeat, and were preparing ot mount a leadership challenge and evict Corbyn, or break away and start a new formation within the party. But whatever long game insiders might have been playing, what we've seen is that many voters are unwilling to gamble with the fate of the country and give Theresa May a blank check for hard Brexit and more cuts.

Krieg: What should progressives in the US -- now in the midst of that "civil war" you described -- learn from the Corbyn wing of Labour in Britain, which, even if they fall short on Thursday, succeeded in grabbing hold of the party and then delivering such an ambitious manifesto/platform?

Sandberg: I think the biggest lesson is that giving people the stuff they need -- and being very clear and straight-forward about it -- can trump even a relentless campaign of fear-mongering and propaganda.

Every single day, the right-wing tabloid press runs breathless headlines trying to incite fear of a Labour government. And Corbyn hasn't always made it easy for himself; he calls it like he sees it, and often gives nuanced, real answers to tough questions, instead of polished soundbites. And there are a lot of people who are not necessarily drawn to vote Labour because of any personal charisma or individual qualities about Corbyn. But they can look at what both major parties are offering and very easily see who is going to make life easier for people like them, and who is going to make it much more difficult.

It's also important to note here where Corbyn's manifesto differs from what centrists might have offered. He's fighting for a redistribution of power in society, not just offering charity to the very poor and leaving the existing balance of power untouched.

Krieg: In the Trump era, the American left (broadly speaking) feels besieged on just about every issue. But the AHCA, or Obamacare repeal, seems to have been the most galvanizing issue so far. How big of an issue is the NHS and health care generally in the UK right now?

Sandberg: It's probably the biggest evergreen issue here.

People love the NHS, and even Conservatives have to pay lip service to protecting it. The only American institution I can compare it to is Social Security, but the reverence people have for the NHS runs so much deeper, because everyone interacts with the NHS throughout their lives, and they rely on it. It's also a major employer, and it has a physical presence in every community. People are truly proud of it. I've seen people jogging in London parks wearing "I <3 the NHS" T-shirts. In 2012, when London hosted the Olympics, there was a huge celebration of the NHS as part of the opening ceremony with thousands of dancers spelling out "NHS" in huge letters in the stadium.

In an era when the Conservatives (and some liberals) are trying to privatize many public services, the NHS is a beacon of how the public sector can work, and in a country where many are uncomfortable with overt displays of nationalism due to the legacy of colonialism, it's probably the most potent symbol of national spirit and collective purpose that everyone can agree on.

Krieg: We've heard a lot about the rise of right-wing populism in Europe. Brexit obviously comes to mind. Then Trump won the presidency here and there was a feeling that the wave had crossed the Atlantic. But you've worked a lot in the US on progressive issues, now also in the UK, and you've met with Spanish leaders -- how does the left-wing global populist movement stack up?

Sandberg: The common thread I see emerging is a recognition that the only thing that can stop rising ethno-nationalist movements that threaten our basic democratic values is a politics that:

Acknowledges that our system is failing the majority of people. Lays the blame where it really belongs -- with the billionaires and the bankers, not immigrants or people of color. Offers a transformative vision to actually rebalance power in society.

The status quo is broken and people are open to radical alternatives -- even dangerous, hateful ones. Centrists on both sides of the Atlantic don't seem to understand how deep this current runs. They seem to be waiting for a return to normalcy without realizing that people who voted for Brexit or Trump are not an isolated fringe who can be banished to a desert island, and that there is substantial dissatisfaction even among people who they consider to be in their camp.

The zero sum mentality -- that if you win, I lose -- is much more pernicious than they would like to admit, and that's what we have to confront. And you just cannot do that if you insist that everything is fine, or refuse to hold anyone responsible. In the US, Democrats responded to Donald Trump with the slogan, "America is Already Great." And Tom Perez recently refused , very awkwardly, to say that Democrats need to name an enemy.

In the UK, again and again since I've been here, people have told me they hold Ed Miliband responsible for Labour being out of power, because he accepted the Conservative logic that austerity was necessary, and didn't hold the banks accountable for the financial crisis.

In contrast, you have the concept that Podemos , the left populist party in Spain, talks about a lot -- and that I think both Jeremy Corbyn and Bernie Sanders also embody -- that there is always an antagonism in society, and our task is to define what that antagonism is: to show that the real battle is not between white people and people of color, or immigrants and the native-born, but between between the people and the billionaires, the many and the few.

We're in a fight for the common sense of society. That may sound lofty or difficult to a lot of people, but when we're faced with catastrophic climate change, extreme wealth inequality, and a fraying social fabric, defending a failed status quo is no longer an option.