Four months into the primary calendar, most of the battlefield is set in the race for control of the US Senate. Now the real fight begins.

Democrats are increasingly bullish about their chances to win back the Senate majority for the final two years of President Donald Trump’s term even as the party faces a difficult map and questions about some of its candidates in key contests. To be successful, Democrats will need to defend all their seats and flip four others, including many in deep-red territory.

Strong recruitment in several key races and a favorable national political environment are fueling the hopes of Democrats. There is widespread disapproval of Trump’s handling of the economy and the war in Iran. Just 34% of the American public holds a favorable view of the president, according to a recent CNN poll.

Republicans hope Trump’s Iran agreement, which remains the subject of talks, could soon ease some of the economic fallout from the war, including the high gas prices that have heightened cost-of-living concerns for Americans. Given the volatility of the war over the past few months, there’s no guarantee that will happen before Election Day.

On Tuesday, the Supreme Court also injected a fresh element into this year’s elections, paving the way for the party committees to spend more money in close coordination with campaigns, a move that experts say could benefit the GOP in the midterms.