As soon as the new Middle East peace initiative was announced, it was clear that violence by its opponents would follow. Less clear was whether those who have backed the road map would have the political courage to withstand the assault.

The deadliest blows so far have come from Palestinian terrorists. Yesterday, a Hamas suicide bomber killed at least 16 people and wounded nearly 100 on a rush-hour bus in central Jerusalem.

But the gravest political damage is being done by Israel's prime minister, Ariel Sharon, whose reflexive military responses to terror threatens to undermine the authority of Mahmoud Abbas, the moderate new Palestinian prime minister. Ignoring strong pleas from Washington, Mr. Sharon has now twice ordered Israeli forces to rocket cars carrying suspected Hamas militants in the Gaza Strip.

Challenging the new Palestinian leadership to take over security responsibility for Gaza is one of the first concrete tests of the road map. Sending in Israeli forces as if nothing had changed needlessly damages the credibility of Mr. Abbas and of the whole Bush peace plan. If it is not evident to Mr. Sharon by now that military reprisals alone can never bring Israel security from suicide bombers, the White House must do all it can to help him understand.

Nobody expects Israel to tolerate terror against its people. But terror can be more effectively rooted out if responsible Palestinian leaders like Mr. Abbas are strengthened, not undermined. It is easy to see why Hamas would like to make Mr. Abbas look irrelevant. But Israel should be doing all it can to strengthen his hand because in the long run that is in Israel's own interest.

For years, Israelis rightly complained about Yasir Arafat's equivocating attitude toward terrorism. The Bush administration has acted on those complaints and worked hard to marginalize Mr. Arafat. As a result, a far more credible figure, Mr. Abbas, is now the Palestinian prime minister. Meeting with Mr. Bush and Mr. Sharon in Jordan last week, Mr. Abbas bravely uttered the unambiguous words Mr. Arafat seemed chronically unable to pronounce. He renounced "terror against the Israelis wherever they may be," a phrase that included soldiers and settlers. Such forthright language was encouraging, though language alone will not be enough. Now Mr. Abbas must be given a chance to follow up his words with effective police action.

The obvious place for him to start is Gaza, where Hamas is based and where the Palestinian Authority's security forces are strongest. To build a Palestinian political consensus against terror, Mr. Abbas needs to show his people that his conciliatory words have brought a change in Israeli behavior. Regrettably, Mr. Sharon's latest actions demonstrate just the opposite.