ust a day after Mr Trump gave a speech on immigration and national security that included sweeping condemnations of Mr Obama’s policies, the president responded with some of his harshest criticisms to date.

起先川普就移民和国家安全问题发表了一份演说，他对于奥巴马的政策给与了彻底的谴责，然而仅仅一天之后，奥巴马就用他迄今而至最为严重的批评做了回应。

"Where does this stop?" Mr Obama asked. "The Orlando killer, one of the San Bernardino killers, the Fort Hood killer - they were all US citizens. Are we going to start treating all Muslim-Americans differently? Are we going to start subjecting them to special surveillance? Are we going to start to discriminate [against] them, because of their faith?"

奥巴马问到：“什么时候才是个头啊?奥兰多案凶手、圣贝纳迪诺案的一名凶手、胡德堡案凶手--他们都是美国公民。我们现在要开始对所有穆斯林美国人区别对待了吗?我们现在要开始对他们进行特别监视了吗?就因为他们的信仰，我们现在就要开始对他们进行歧视了吗?”

Such views, Mr Obama said, are "not the America we want".

奥巴马说，这些论点“不是我们想要的美国”。

As the Obama-Trump clash heats up, here are several things to keep in mind.

随着奥巴马和川普之间的对决逐渐升温，有几件事我们需要铭记在心。

Donald Trump and Barack Obama have a history that predates the current election cycle. In early 2011 Mr Trump repeatedly circulated conspiracy theories about the authenticity of the president’s birth certificate and whether he was actually born in the US.

事实上在这轮大选开始前，川普和奥巴马之间就结下了梁子。早在2011年的时候，川普就一再流传关于奥巴马出生证明真实性的阴谋论，他甚至怀疑奥巴马不是在美国出生的。

Later that year, at a black-tie Washington event, Mr Obama relentlessly mocked Mr Trump while the New Yorker sat stone-faced in the audience - a performance the New Yorker’s Adam Gopnik said helped motivate Mr Trump to eventually run for president.

那年晚些时候，在华盛顿一场正式活动上，奥巴马无情地嘲弄了川普，当时川普面色铁青地坐在宾客中间--据亚当·高普尼克透露，正是那场活动让川普最终下定决心竞选美国总统。

Over the past year Mr Trump has questioned Mr Obama’s competence and openly speculated about his allegiances in what he labels the war on radical Islam. As recently as Sunday, he cryptically noted that Mr Obama was either "tough, not smart, or he’s got something else in mind".

在过去的一年里，川普质疑了奥巴马的能力，并将其所领导的战争打上了“激进伊斯兰”的标签，公开质疑奥巴马对国家的忠诚。就在上周末，他隐晦地指出奥巴马既不“强硬，也不聪明，脑子里什么其他东西都没有”。

Mr Obama has criticised Mr Trump in the past, but his remarks on Tuesday were the sharpest, most direct of this political season. His tone was stern, his language blunt.

奥巴马之前也曾批评过川普，但是周二的讲话是他这一任期内最尖锐、最直接的发言。他的语气很严厉，他的措辞很直接。

A few hours later, Mr Trump shot back, effectively accusing Mr Obama of treason.

几个小时之后，川普反击了，直截有力地指控奥巴马叛国罪。

The president, he said in an email to the Associated Press, "continues to prioritise our enemy over our allies, and for that matter, the American people".

在发给美联社的一份邮件中，川普说总统“继续把我们的敌人摆在优先于我们盟友的地位，更甚者，摆在优先于美国人民的地位”。

The president clearly does not like the presumptive Republican nominee - and the feeling appears to be mutual.

很明显奥巴马总统不喜欢这位共和党假定候选人--而相互的，川普也不喜欢奥巴马。

There’s very little precedent in modern US political history for a sitting president to directly and sharply criticise the opposing party’s standard-bearer in the run-up to a general election.

在美国现代政治史上，很少有现任总统在大选开始前，直接、尖锐地批评反对党的候选人的先例。

In part that’s because there simply haven’t been many two-term presidents in recent memory - George W Bush, Bill Clinton, Ronald Reagan and Dwight Eisenhower are the only ones since World War 2. And of those, only Reagan and Eisenhower left office with high approval and largely free from scandal.

一部分原因是因为近年来，没有多少连任两届的美国总统--乔治·W·布什、比尔·克林顿、罗纳德·里根和德怀特·艾森豪威尔是二战以来仅有的几位连任两届的总统。在这些人之中，只有里根和艾森豪威尔在卸任之时获得了很大的赞誉，并且几乎没有丑闻。

Mr Obama is currently above 50% in most opinion polls and has been trending upward, so he is in a position to be an active and eager participant in the campaign fray. Because he’s not the nominee, he has a free hand in what he can say, and he can bring the full weight of the presidency to bear on Mr Trump.

在大多数民调中奥巴马的支持率都在50%以上，并且这一数据一直曾上升趋势，所以他将来能够在竞选辩论中成为一个积极、热心的参与者。因为他不是提名人，所以在他的发言上没有束缚，而且他可以调动身为总统的所有优势来击败川普。

The Republican nominee will be effectively campaigning against two candidates - Mrs Clinton and Mr Obama. And, at least for now, Mr Trump can only count on the tepid support of many of his fellow Republicans. Following Mr Obama’s remarks on Tuesday, the Republican National Committee issued a press release that made no mention of Mr Trump or his proposed immigration measures, instead focusing on the Second Amendment and firearm rights.

川普实际上将要和两位民主党候选人竞争--希拉里和奥巴马。然而，至少从现在来看是这样，川普只能够依靠他众多共和党同僚不温不火的支持。在奥巴马于周二发表讲话过后，共和党全国委员会发布了一篇新闻稿，新闻中没有提及川普和他提出的移民措施，反而关注于宪法第二修正案和枪支权利。