Merger and acquisition (M&A) deal value in the U.S. in the three months to the end of June slipped to its lowest quarterly total since 2013 as a lack of clarity over President Donald Trump's hoped-for corporate reforms hit buyer appetites.

Despite heady promises made during last year's election campaign and in the early days of his presidency, Trump's administration has so far failed to deliver on his widely heralded tax and antitrust amendments.

The slowdown in U.S. deals in the first half of the year saw the region notch up 2,446 announcements at a total value of $602.6 billion versus 2,677 announcements at a total value of $588.5 billion a year ago, according to data released Tuesday by Mergermarket. This led to the region's share of global activity slipping by 2.4 percent to 40.4 percent for the period.

Just as political instability ratcheted up in the U.S., across the proverbial pond a perceived dissipation of political and economic concerns helped Europe to pick up the mantel and deliver a bumper first half for the region. Activity surged by over 30 percent year-on-year with $481.9 billion worth of deals announced as euro zone sentiment was boosted by French President Emmanuel Macron's decisive victory in May and an ongoing stabilization in regional economic data.

"Political changes always threatens M&A activity and we've seen how more stable situations in Europe can lead to growth in the M&A market. In terms of the U.S., we've seen dealmakers start to hold off as they wait to see how issues such as tax reform and the potential repeal of Obamacare develop," said Jonathan Klonowski, EMEA research editor at Mergermarket.