Angry Trump says Moscow ties at ‘very dangerous low’

WASHINGTON — Special counsel Robert Mueller is using a grand jury in Washington as part of an investigation into alleged coordination between the Donald Trump campaign and Russia, a source familiar with the probe said on Thursday.

The use of a grand jury, a standard prosecution tool in criminal investigations, suggests that Mueller and his team of investigators are likely to hear from witnesses and demand documents in the coming weeks and months.

The source, who confirmed that Mueller had turned to a grand jury, is not authorized to discuss the investigation by name and spoke on condi-