10 things you need to know before the opening bell

Here is what you need to know.

Germany says Trump has "weakened the West." German Foreign Minister Sugmar Gabriel unleashed on President Donald Trump saying that "anyone who accelerates climate change by weakening environmental protection, who sells more weapons in conflict zones and who does not want to politically resolve religious conflicts is putting peace in Europe at risk," according to AFP.

A crackdown on China's "shadow banking" system is rattling its markets. Since Guo Shuqing was named banking regulator in February, he has introduced rules to discourage banks from using borrowed money to invest in bonds, which in turn has pushed bond yields to two-year highs and wiped $38 billion in market cap from Chinese banks.

Greece wants clarity on its debt. Greek Finance Minister Euclid Tsakalotos pushed back against a report from Germany's Bild that suggested Greece would default if debt relief was not granted telling Reuters, "What I did say is that the disbursement was not an issue, because all sides agreed that we have kept to our commitments. But the Greek government feels that a disbursement without clarity on debt is not enough to turn the Greek economy around."

The polls are tightening ahead of the UK election. A poll conducted by Survation for ITV's Good Morning Britain shows Prime Minister Theresa May's Conservative Party holds a 43% to 37% lead over Jeremy Corbyn's Labour Party ahead of the June 8 election, the Independent says. That gap has narrowed by three points over the past the week.

Gold hit a 1-month high. The precious metal crossed $1,270 an ounce on Tuesday morning, hitting its best level since April 28.

Oil is slipping. West Texas Intermediate crude oil trades down 0.4% at $49.57 a barrel as traders remain skeptical that the extension of the OPEC production cuts through the first quarter of 2018 will be enough to cure the global oil glut.

Mark Yusko is sounding the alarm on US stocks. Speaking at the Mauldin Economics' Strategic Investment Conference last week, Morgan Creek Capital Management CIO Mark Yusko said, "I'm telling you right now, the US is going to have a crash and it will be massive."

Stock markets around the world are lower. Japan's Nikkei (unch) finished flat and France's CAC (-0.6%) trails in Europe. The S&P 500 is set to open lower by 0.2% near 2,410.

Earnings reporting is light. Dollar General reports ahead of the opening bell while Hewlett Packard Enterprise and Restoration Hardware release their quarterly results after markets close.

US economic data flows. Personal income and spending and PCE core prices will be released at 8:30 a.m. ET before S&P Case-Shiller home prices and consumer confidence cross the wires at 9 a.m. and 10 a.m. ET, respectively. The US 10-year yield is down 1 basis point at 2.24%.